This paper introduces the automatic monitoring system on inner observation of a hydropower station， especially describes lightning ?proof measures that have been used in the system. Several lightning strokes to ok place in August, 2007. By means of analysis, it is concluded that the causation is lightning stroke to be led into inner of equipments through the shield-lines of the sensors so as to damage equipments. Some measures to improve the lightning proof capability of the automatic monitoring system were taken, and they are in perfect order at present.