[[abstract]]Since march 1998，health insurance revenue is far less than health insurance medical expenditure, the health insurance system would crush finally.Therefore, to build the health insurance medical expenditure forecasting model is the present urgent job for the national health insurance institution. According to the historical research, the medical expenditure would be affected by the demography , GDP/ per capital , unemployment rate , and inflation rate (Newhouse；Gerdtham ；Hitiris and Posnett). For these reasons, when health insurance institute want to establish the medical expenditure global budget plan, it should take into account those effective factors. The purpose of this research are as follows: (1).Forecasting the medical expenditure by time series model. The medical expenditure acts as the endogenous variables and the demography, medicine resources, and macroeconomic factors act as the exogenous variables. (2).Finding the linear significant marginal affects of the explanation variables and their correlations by ordinary lease squares (OLS). (3).Allocating the medical expenditure global budget by investigating the significant factors in the research. (4).Assess the current health insurance rate-making rationality according to the health insurance medical expenditure forecasting model of this research with the health insurance salary scale.