The limiting resolution of an AlGaN photocathode image intensifier tube is much less than the limiting resolution of a GaAs photocathode image intensifier tube; thus, based on the effect of ultraviolet fluorescence, we calculate the limit resolution of an AlGaN photocathode and promote its ultraviolet modulation transfer function. According to the proximity focus system modulation transfer function and the test result of the custom developed AlGaN photocathode image intensifier, the resolution model of the AlGaN photocathode image intensifier is established. By comparing the ultraviolet modulation transfer function with the proximity focus system modulation transfer function, we discovered that the ultraviolet and photoelectron transmission in an AlGaN photocathode can reduce the limiting resolution of the AlGaN photocathode image intensifier tube and that the main reason affecting the limiting resolution of the AlGaN photocathode image intensifier tube is the photoelectron transmission and the scatter in the AlGaN photocathode.