In recent years, the internet has been used in almost every aspect of life, and the demands for communication capacity and transmission speed are increasing. The unit device technology has basically matured, but how to maintain the good performance of unit devices and place multiple devices on the same chip to solve the bottleneck of the current communication system is still under study. Nowadays, electro-optical modulators and wavelength division multiplexers with various structures have been proposed. Research on these two types of single devices has become increasingly mature, but there are few studies on silicon-based optoelectronic integration that integrating the two devices to achieve multiple functions, which means more research on integrated devices is still needed. Considering the requirements of optical inter-connected networks and data centers for small size, large bandwidth and integration, we propose an on-chip integrated device for electro-optic modulation and wavelength division multiplexing. The two devices are cascaded together using silicon waveguides, which has the characteristics of small size, small modulation voltage, low insertion loss, low channel crosstalk and large modulation depth.In this paper, an integrated device based on photonic crystal nanobeam cavity electro-optical modulator and wavelength division multiplexer is proposed. Both the electro-optical modulator module and the wavelength division multiplexer module are composed of a one-dimensional photonic crystal nanobeam cavity. The integrated device consists of nanowire silicon waveguide, one-dimensional photonic crystal nanobeam cavity, Al electrode, and silicon dioxide cladding. Among them, the nanowire silicon waveguide, the one-dimensional photonic crystal nanobeam cavity, and the Al electrode are located in the silicon dioxide cladding. The whole integrated device can realize the "on" and "off" state modulation of different wavelengths of the electro-optical modulation module and download different wavelengths through the wavelength division multiplexing module. In this paper, simulation analysis is carried out based on the FDTD module and Device module in the commercial optical simulation software Lumerical. First of all, by analyzing the side-coupling structure of the one-dimensional photonic crystal nanobeam cavity, the parameters affecting its transmittance and resonance wavelength are found. Afterwards, based on the plasmonic dispersion effect, wavelength modulation is realized through the nanobeam cavity and the PN junction to complete the design of the electro-optic modulation module. Then based on side-coupling theory, wavelength division multiplexing is realized through the nanobeam cavity to complete the design of wavelength division multiplexer module. In the end, the two modules are integrated together. Since the resonant wavelength of the nanobeam cavity will shift after integration, the nanobeam cavity is fine-tuned to complete electro-optic modulation and wavelength division multiplexing at 1 550.4 nm and 1 553.6 nm.The integrated device has great performance. It has small modulation voltage. When the modulation voltage is 1.25 V, the change in electron concentration $?N_{\mathrm{e}}$ reaches 1.58×10¹⁸ cm^-3, and the change in hole concentration$?N_{\mathrm{h}}$ reaches 1.95×10¹⁸ cm^-3, which can realize the modulation of the wavelength. According to the simulation, the transmittances of 1 550.4 nm and 1 553.6 nm in the "on" state are 81.50% and 91.21%, and the transmittance of 1 550.4 nm and 1 553.6 nm in the "off" state are 1.58% and 0.51%, respectively. It can be calculated that the total insertion loss is less than 0.89 dB, the extinction ratio is greater than 17 dB, the modulation depth is greater than 0.98, and the channel crosstalk values are all less than－23 dB, which indicates the modulation and wavelength division of the device has good performance. Compared to previous research results, it is no longer a single-function device. Compared to other integrated devices proposed in table 2, the wavelength interval of the integrated device proposed in this paper is smaller, and the modulation voltage is also lower, only 1.25 V. In addition, the structure size of the integrated device is smaller, which is beneficial to large-scale on-chip integration.In conclusion, an integrated device based on photonic crystal one-dimensional nanobeam cavity electro-optical modulator and wavelength division multiplexer is proposed, which realizes "on" and "off" state modulation and wavelength downloading at 1 550.4 nm and 1 553.6 nm. The insertion loss of the device at the working wavelengths of 1 550.4 nm and 1 553.6 nm are 0.89 dB and 0.40 dB, respectively. The extinction ratio is 17.13 dB and 22.52 dB. The modulation depth is 0.98 and 0.99 and the channel crosstalk is -24.20 dB and -23.37 dB, respectively. The footprint is 71.34 μm×7.8 μm×0.22 μm. The integrated device has large modulation depth, low insertion loss, high extinction ratio and low channel crosstalk. It also has a compact structure and is easy to be integrated, which can be used in optical inter-connected networks and data centers.