The security problem of the global positioning system （GPS） deception signal transmitted by unmanned aerial vehicle （UAV） to the automatic system in the substation is not clear. This paper proposes a method to evaluate the interference of GPS deception signal to the time synchronization device of substation, and theoretically analyzes the influence of GPS deception signal on the time synchronization device of substation. The spatial distribution of deception signal power intensity and the electric field intensity of unmanned aerial vehicle decoy equipment under different transmitting power are measured. The experiment verifies the influence of GPS deception signal on the quality of the satellite received by the time synchronization device and the accuracy of time service. The influence laws of the transmitting power of the unmanned aerial vehicle decoy equipment and the distance between it and the GPS/BeiDou navigation satellite system （BDS） receiving antenna of the time synchronization device on the time service accuracy are analyzed. The results show that the GPS decoy signal will not make the time synchronization device enter the punctual state when the antenna of the time synchronization device is 10 m away from the unmanned aerial vehicle decoy device. The antenna of the time synchronization device is more than 60 m away from the unmanned aerial vehicle decoy equipment, and the impact of GPS deception signal on the time synchronization device can be ignored, which provides reference for safe and stable operation of substation.