In order to more realistically match the power supply capability of the satellite in-orbit, the research on the energy simulation technology of the small satellite in-orbit is carried out. A set of energy supply simulation system consistent with the in-orbit status of the satellite is constructed to complete the entire simulation from the orbit simulation to the V-I output of the solar array, so that each array can independently simulate the light variation rule in the process of satellite in-orbit, realizing the dynamic power supply output of the solar array simulator. It can provide more real and effective data for the ground test of the small satellite, and thus calculate whether the energy supply of the small satellite in the process of executing the mission in-orbit can meet the demand. It can also provide a design analysis and efficiency optimization support platform for the subsequent in-orbit mission planning and verification. The design method introduced in this paper has been verified by engineering application of several small satellites.