Alkali atom vapor cells are the essential component of quantum microwave measurement equipment. By means of laser pumping technology, alkali atoms can be easily excited from the ground to Rydberg states. Alkali atoms is very sensitive to electric filed because of their very large polarizability, huge electric dipole and low ionization threshold field and so on. Recently, by virtue of the strong interaction of microwave field and Rydberg atoms, alkali atom vapor cells have been widely applied to detect the amplitude, frequency, phase and polarization of electric field, especially the microwave electric field. Quantum microwave measurement technology has shown significant advantages, such as the break of probe size independent of wavelength, extremely high sensitivity and accuracy, very broad spectrum measurement, and very large dynamic range. In the past decade, the technology has shown great potential for application in the monitoring of ultra wide band electromagnetic spectrum, the metering of microwave electric field, microwave imaging and communication, etc. Thereinto, the state population of Rydberg atoms in vapor cell is one of the decisive factors affecting measurement capability. Up to now, certain properties of vapor cell can be obtained by optical or other measurement technologies, such as the thickness, refractive index and transmittance of glass envelope, atomic ratio and density in vapor cells. However, all of them can not directly reflect the Rydberg atomic states in vapor cell, which could give rise to difficulties to the performance optimization of quantum measuring equipment based on atom vapor cells. In this paper, a theoretical calculation model of Rydberg atomic state population excited by two-photon resonance has been established by using the ideal gas state equation, and the Rydberg blockade effect and gas atomic distribution are comprehensively analyzed. Meanwhile, an estimation method of Rydberg atomic state population, which is acomplished by aid of optimal Electromagnetically Induced Transparency (EIT) signal of Rydberg atoms, has been proposed and demonstrated experimentally under shading condition and room temperature, by means of the cylindrical (~1.0 cm in diametre and length) and cuboid (~1.0 cm in width and height, and ~2.0 cm in length) vapor cell, respectively. The vapor cells are filled with saturated cesium (¹³³Cs) atoms at 300 K, and the intensity of pressure is ~6 666.1 Pa. In order to obtain the theoretical calculated and experimental estimates of the Rydberg state population excited by two-photon resonance, the EIT experimental setup has been put up by ~852 nm and ~1 020 nm semiconductor laser. Both of them are produced by TOPTICA Photonics. The typical spectral linewidths (5 μs integration time) of two semiconductor lasers are ~100 kHz. The ~852 nm laser, which is stabilized on the saturated absorption spectral signal of ¹³³Cs D2-line, is employed as a probe laser to irradiate into the vapor cells to excite the ¹³³Cs atoms from the ground state (6S1/2) to intermediate state (6P3/2). Simultaneously, after frequency-doubling of ~1 020 nm laser, the coupling laser in the wavelength of ~510 nm counter-propagates through the vapour cells to excite the atoms from the intermediate state to the Rydberg state (42D5/2). Thereinto, the probe and coupling laser are collimated and linearly polarized. Experimentally, the wavelengths of probe and coupling laser also can be certified by wavelength meter (Bristol 771A VIS). And then, by scanning the frequency of coupling laser and adjusting the laser powers, the optimal EIT spectrum can be displayed on the oscilloscope, which is connected into the photodetector (Thorlabs PDA36A2). The gain (50 Ω) of photodetector is ~7.5×10⁶ V/A, and the responsivity at the wavelength of ~852 nm is ~0.55 A/W. The laser parameters of optimal EIT spectrum can be measured by laser beam quality analyzer (Ophir SP920 s) and power meter (Thorlabs PM160). For the cylindrical vapor cell, the power and 1/e² beam diameter of probe laser are ~13.0 μW and ~886.0 μm, and the ones of coupling laser are ~22.0 mW and ~1 425.0 μm. For the cuboid vapor cell, above-mentioned laser parameters are ~16.2 μW, ~901.0 μm, ~23.5 mW and ~1 437.0 μm, respectively. Comparing the natural linewidth of Rydberg state (42D5/2) and two lasers, the Rydberg blockade radius r_B of 42D5/2 is calculated to be ~6.3 μm. Because of the two-photon resonance, the Rydberg atoms only can be excited in the overlapping region of lasers. According to the ideal gas state equation and dense packing model, a theoretical calculation model of Rydberg atomic state population can be established. So the Rydberg atomic state populations in the cylindrical and cuboid vapor cell can be obtained, 3.06×10⁶ and 6.33×10⁶, respectively. Otherwise, in the optimal EIT spectrum, the energy difference between EIT peak and ground noise can be regarded as the energy of ~852 nm enhanced transmission laser. Furthermore, a photon represents a Rydberg atom at 42D5/2 level. Hence, the Rydberg atomic state populations in two vapor cells can be estimated to be2.32×10⁶ and 5.86×10⁶. The experimental results are in good agreement with the values calculated by aforementioned theoretical model. The theoretical model and measurement method is benefit to characterization and optimization of vapor cell properties, which can promote the rapid development of quantum microwave measurement technology based on Rydberg atoms in future.