Abstract: This paper introduces the concept of measurement uncertainty to its assessment method to achieve the development of national unity.It points out the uncertainty of measurement involves the technical specifications at home and abroad, given the uncertainty, the definition of error, accuracy and precision of several concepts and analysis of their relationship.Then, two methods of evaluation of uncertainty are given, they are a kind of evaluation method and class B evaluation method, especially summarizes the concrete steps of Class A evaluation method.Finally, it summarizes the six specific evaluation steps of uncertainty: Mathematical evaluation model is set up; Strives for the best estimate; Standard uncertainty components; Synthetic standard uncertainty.Finally, the expanded uncertainty put forward the report of uncertainty.