In view of the propagation characteristics of Q-band communication links that were severely affected by conditions such as rainfall, fog and atmospheric absorption, based on the analysis of the propagation loss of the Q-band geostationary satellite orbit downlink, the influence of rainfall attenuation on the I/N distribution under the interference scenario of the earth station co-location was studied. A method to calculate the propagation loss of Q-band downlink combined with rainfall distribution was proposed, and a functional model for I/N combined p% that the percentage of time when rainfall attenuation exceeds a threshold value was established. The influence of p% on the distribution of I/N was analyzed, and the average annual interference distribution was forecast. This method was used to analyze the influence of the CHINASAT-G-115.5E satellite network which was registered by the ITU, and the results show that the lower the p%, the more obvious the influence of rain attenuation on the communication link. When p＜0.5, the attenuation threshold changes faster. When the location of earth station and the orbit longitude of the interfering satellite are fixed, the smaller the p%, the smaller the minimum value of I/N in the annual average 1-p% time. This method can be applied to study the interference distribution of other orbital satellites, and provide a reference for interference avoidance.