Micro-channel Plates(MCPs) are an important part of ultraviolet photon counting imaging detectors. They can intensify single particles or photons by the multiplication of electrons via secondary emission.Thus, the MCP gain has an very important influence on the performance of ultraviolet photon counting imaging detectors. In this article, influence of MCP gain on decoding accuracy is studied by using Monte Carlo method. Simulation results show that decoding error is large when MCP gain is low,and MCPs shoud have at least 106 gain to ensure accurate decoding. At the same time, influence of MCP gain on decoding error was tested by using ultraviolet photon counting imaging system based on TWA(Tetra Wedge Anode,TWA). Experimental results are consistent with the theoretical analysis and simulation. © 2019 SPIE.