Evaporation of monomethyl hydrazine(MMH)at high pressure is studied. The MMH droplet radius and temperature at different environmental pressure is computed and compared. The evaporation constant. the number of heat transfer and the number of mass transfer.are considered and computed. The results are identical to the test data. The effect of Lewis number to the limit pressure of evaporation is evaluated. It shows that the evaporation model and compute method are reasonable. The results are important for the analysis of the combustion process in liquid rocket engine. This method may be used to evaluate other fuels.