A key technology of γEMP as sorted simulator is the synchronous operating between the γsimulator and the EMPsimulator.This paper analyzes the requirement of the assorted simulator to the synchronous capability of γsimulator and points out that the time jitter ΔTγ in γsimulator should reach to the level less than half width at half maximum of γpulse. Then, the difficulties and the methods of improving synchronous capability of FlashⅠ γsimulator are analyzed and reseached. The synchronous capability and feasibility of Flash1A as the γsimulator in the γEMP simulator system are discussed aslo.