Abstract: In order to study the effects of random heat source on discharge pits and workpiece surface forming in Short electric arc machining（SEAM）, the temperature field model of random heat source in Ti-6 Al4V SEAM was established. By introducing the random discharge function to simulate the randomness and complexity of discharge in SEAM, the formation and superimposition of discharge pits were studied. The forming process of workpiece surface was revealed, and the effect of electrical parameters on the surface topography was studied. The results show that it is difficult to find the complete single pit because of the randomness of the discharge, which make the surface of the workpiece disorderly superimposed by numerous discharge pits, and the machining accuracy improves under the conditions of low voltage, high frequency and small duty cycle,then,the better surface quality of workpiece can be obtained.