Abstract: Resolution and MTF are two important parameters for an image intensifier. Up to now, there is no unified understanding on the primary electronic energy distribution from generation Ⅲ image intensifier cathode, and no wellestablished theoretical model on resolution and MTF. A resolution calculation model under a specific condition was obtained by theoretical analyses and assumptions. The theoretical resolution value was obtained by substituting the measured parameters such as 1st proximity distance, 2nd proximity distance, photocathode voltage and phosphor screen voltage into the resolution calculation model. By comparing it with the measured value, it is found that the value of deviation between the calculated and the measured resolution values is less than 12.3%. The method and results are helpful for people engaged in the design of generation Ⅲ image intensifier.