Abstract: Main hoist remain coal when working abnormal situation this cause the skip bucket leaving to reload and the hoist can't work., we will do the technical improvement for this. After observation, we found the current of constant velocity is smaller showed on the monitor screen before the reload, so we add a protection by change the PL program in order to supervise the current situation. We successfully avoid more than 100 the similar accidents after carry out this protection, this help us reaching our aim to avoid the main hoist reload.