Aiming at the problems of difficult real － time monitoring of the safe distance between crane bucket arm and live equipment，and many obstructions in the process of substation maintenance，the virtual " mouth" three － dimensional space is constructed by setting boundary points． The crane bucket arm works in the " mouth" space． UWB positioning module is used to collect the distance of the bucket arm from the set boundary points in real time and transmit it to the device backstage． The space triangular cone model is used to calculate the safe distance between bucket arm and live equipment． Comparing the testing distance with safe distance，the alarm function is realized when the testing distance is less than the safe distance．