Rod pinch diode (RPD) has the characteristics of small focal spot and high brightness, which is a research hotspot in the field of flash radiography. In this paper, based on the Marx generator and pulse forming line technology route, 1 MV high voltage pulse driving RPD is generated, and the experimental research of diode with different structure parameters is carried out. Based on the numerical model of RPD physical process, the ratio of cathode to anode aperture is a complex variable related to the average diffusion velocity of cathode and anode plasma, which is also the main parameter affecting the radiation performance of RPD. The results show that the average diffusion velocity of RPD anode plasma is about 0.6 cm/μs at 1 MV voltage. When the anode rod diameter is fixed, the diode numerical model shows that reducing the cathode aperture can make the diode enter the strong pinch state faster, but too small cathode aperture will lead to premature closure of the diode gap.