Abstract: Temperature-differential method is one of the two methods to field-test the efficiency of pump in oil transportation system. Based on the error theory, this paper analyzes the main factors to influence the test results, that is, the accuracy of the outlet pressure gauge, densimeter and temperature-differential meter as well as the errors of installment of the inlet and outlet thermometers. It comes to the conclusions: (1) unlike water-flooding pump, the measurement error of the oil density cannot be neglected in efficiency fieldtest of the pump; (2) when the inserting length of the cannula of thermometers is not deep enough, the errors of installment of the inlet and outlet thermometers are the main factors to influence the measurement result of the efficiency of the water-injection pump and (3) in order to decrease the measurement errors in the efficiency field-test of pump, the accuracy of the outlet pressure gauge, densimeter and temperature differential meter must be increased, and the depth of the cannula of thermometers mustt be ensured.