Accurate evaluation of voltage sag is the basis for improving and resolving sag problems, and testing of evaluation methods is a guarantee of quality. Aiming at the problem that the existing sag index system lacks comprehensive evaluation method and the evaluation result cannot be quantitatively tested, this paper proposes a set of grid node voltage sag comprehensive evaluation process and its testing method based on IEEE Std 1564-2014 index system standard. Firstly, in view of the current sag evaluation, only the sag frequency or amplitude is evaluated to cause the lack of information. This paper establishes a mathematical model of sag comprehensive evaluation from the aspects of sag frequency, amplitude, energy and severity. Secondly, this paper proposes a general process for comprehensive evaluation of voltage sag with key links such as index preprocessing, index weighting and results testing. Finally, this paper proposes a comprehensive evaluation process testing method, from the perspectives of identification, consistency, stability and effectiveness, quantitatively testing of all aspects of the comprehensive evaluation. The comprehensive evaluation results can reflect the nodes or regions with severe sag in the power grid. The testing method can measure the advantages and disadvantages of different evaluation methods, thus providing a scientific basis for the analysis and treatment of sag. Based on the Monte Carlo method, the IEEE 30-bus system is simulated to verify the rationality and accuracy of the proposed method.