【摘要】The size of fiscal expenditure reflect the degree that government intervene in m a rket, if government intervene in market too much, the action of government will lower economic growth.In order to choose optimal size of fiscal expenditure,the paper developed a endogenous growth model including government, and estimated th e optimal size of fiscal expenditure in china from experience, the period is fro m 1978 to 2000.The conclusion is the optimal internal budget size of fiscal expe nditure is 21 2%(fiscal expenditure relative to GDP),the total optimal size of fiscal expenditure is 24%(the total fiscal expenditure relative to GDP).