In response to the issue of single detection methods during air gap discharge development, which fail to comprehensively reflect parameter characteristics of the discharge process, this study investigated the variations of relevant physical quantities during oil-paper insulation air gap discharge and elucidated the relationship between different characteristic parameters and the development stages of air gap discharge. The effectiveness of different detection methods was experimentally compared, and the signal characteristics of different monitoring quantities at different development stages were analyzed. Corresponding physical descriptions and stage characteristics were provided. The results indicate that, under oil-paper insulation air gap discharge defects, different monitoring methods exhibit varying sensitivities, with pulse current demonstrating the highest sensitivity. Through analysis of various characteristic parameters, the air gap discharge development process can be divided into initial discharge, sustained discharge, and pre-breakdown stages. Compared to single-method detection, the comprehensive use of multiple discharge signals can more effectively assess the severity of fault development.