In this paper, we investigate the relationship of heating current in Electric Hot Machining with tool life, cutting parameters and machined surface roughness. Experimental results indicate that there is an optimal heating current in EMH in which the effect of hot machining is the best. A method of rapid determining the optimal heating current under various cutting conditions in EHM is proposed according to the conservation law of optimum cutting temperature. That is, for a certain combination of tool and workpiece, the heating current relative to optimal cutting temperature in different conditions can be found by changing heating current and measuring cutting temperature to meet the control object of temperature in EHM. The PID control principle and effect of computer monitoring system for realizing optimal heating current control in EHM is also introduced.