Abstract: The vacuum environmental radiation is very severe and the surface of plate can not be destructed for electron beam selective melting forming,so the method combined therm-couple measurement and numerical simulation was used to obtain temperature field of plate's surface under electron beam preheating.Measurement results of thermocouple were utilized to optimize the heat efficiency,depth of electron and thickness of plate,consequently get reasonable simulation program.Temperature of plate's surface was forecasted by simulation program and optimized factor level.Results showed that the higher accuracy of surface temperature could be obtained by the numerical simulation combined with temperature measurement by thermal couple.When temperature of plate' surface reached 800℃ which is as same as sintering temperature of titanium alloy powder,preheatingtime of electron beam was 1 600 s.