The present invention discloses a method for analyzing reliability of a transformer based on service year and load level, comprising the following steps: (1) determining load levels of transformers; (2) determining load values of the transformers in an original state; (3) obtaining hot-spot temperatures of the transformers; (4) obtaining insulation lives of the transformers according to the hot-spot temperatures of the transformers; (5) obtaining a failure probability cumulative distribution function of the transformers; (6) obtaining an average failure rate index of the transformers in the original state and an average failure rate index of the transformers in a failure state; (7) obtaining a cascading failure starting probability index Pic and a cascading failure weak link indicatrix Pvc, and identifying the transformers in a critical state in a system by sorting of the Pic and the Pvc. The method provided by the present invention improves accuracy of analysis for the reliability of the transformers in the case of cascading failure by combining influences of self structures, functions, service years of the transformers and a coupling relation between the transformers in a regional power grid on equipment reliability.