Abstract: In this paper, the evaluation method of the uncertainty of measurement results of 4109 synthetic lubricating oil kinematic viscosity measurement is introduced.The sources of uncertainty are evaluated from each step of the measurement procedure, and the main uncertainty component in the process of kinematic viscosity measurement is analyzed..Uncertainty evaluation shows that the repeatability of measurement and test, such as temperature sensor, measurement time, viscometer constant have certain influence on the test results, therefore in the process of test we should carry on the test strictly in accordance with the standard test process to improve the test accuracy.