The invention provides a state evaluation method and system for a high-voltage large-capacity STATCOM (Static Synchronous Compensator). The method includes S1, establishing a first-level evaluation model and a second-level evaluation model and grouping devices of the STATCOM according to basic characteristics of the different devices; S2, according to the first-level evaluation model, collecting state information of the different grouped devices preliminarily as first-level evaluation indexes for performing first-level evaluation calculation on the grouped devices successively and obtaining the failure rates of the grouped devices; S3, if whether the grouped devices meet failure or not cannot be judged accurately according to the failure rates, further collecting the state information of the grouped devices as second-level evaluation indexes for calculation according to the second-level evaluation model, and determining the failure devices and reasons. According to the invention, through establishing the evaluation models of the two levels and selecting partial indexes in each model of each evaluation model for calculation and analysis, the evaluation process is simplified and resource waste is avoided.