Abstract: Operating under variable conditions will affect the efficiency of the crude oil heater seriously. Check thermal calculation under variable conditions is done based the heater counter-balance energy efficiency in this paper. The model that predicts the exhaust gas heat loss of the heater is deduced by the method of deviation analysis. And the comprehensive influence of exhaust gas temperature and excess air ratio to the heat efficiency is analyzed quantitatively. So it can provide prediction of the variable operating results for the in-site manipulation, and the energy loss section can be found correctly. It can also help the operator to adjust the operating parameters to realize the heater running safely and economically.