Most of the calibration experiments of the electric field probe only consider the influence of the structure and performance of the TEM cell. In the calibration experiment, the placement of the probe makes the calibration result produce a large deviation. Therefore, the main reason for the error is the size of the probe, rather than the TEM cell. Taking the actual model and electric field probe into account, in this paper, the radiation field distribution of TEM cells with different structures and sizes is studied from the time domain perspective based on open TEM cells, while the S-parameters of TEM are analyzed from the frequency domain perspective using 3D electromagnetic simulation software. In addition, this paper compares the errors before and after the probe is placed in the chamber, and introduces the electric field calibration formula based on the calculation results. In order to improve the influence of the probe on the electric field, a new structure was designed. The results show that the new structure not only guarantees the bandwidth, but also improves the uniformity of the electric field and the accuracy of the probe calibration, which provides a new idea for the design of the TEM cell and the calibration of the probe.