Abstract: Gas relay is an important non-electrical protection device in transformers, while the existing gas relay cannot timely judge the transformer fault degree after a heavy gas alarm. This paper proposes a recognition method for the transformer heavy gas fault degree based on the gas relay baffle operating time T₁ from the starting angle to the heavy gas action angle and the baffle holding time T₂ of the heavy gas alarm state. First, the force of the gas relay baffle is analyzed, and the operating characteristic equation of the baffle under the oil flow is derived. Then a new type of gas relay with real-time output baffle rotation angle and an experimental platform with functions of simulating the gas relay baffle operating time characteristics under different fault degrees are developed. The gas relay baffle operating time characteristics of T₁ and T₂ are further measured on the experimental platform. The results show that T₁ gradually decreases but T₂ gradually increases with the development of the transformer heavy gas faults degrees. Based on the change trend of T₁ and T₂, the transformer's heavy gas fault degrees can be identified, which provides an effective method for the transformer heavy gas fault degree identification.