Strategy use is a mental operation which aims directly at its target. In order to investigate brain activity during mental arithmetic strategies using, subtraction answers-discrimination tasks were used through 8 healthy subjects with the Event-related Potentials (ERPs) technique. The results showed: (1) The principal components of ERP were: N1, P1, P2, P300 and N400. (2) At the F3, C3 point, stage 4 induced more negative wave than stage 1; At F4, C4, P3 and P4 point, stage 4 induced more positive wave than stage1. (3) Activation of brain areas mainly included Temporal lobe, Prefrontal cortex and Parietooccipital. (4) With the subjects gradually skilled in using strategies, activated brain region gradually moved from back to front; meanwhile the right side had higher active level than the left of brain. Further exploration need to describe more detailed brain potentials during mental arithmetic strategies using in other conditions.