The invention discloses an oil paper insulation early stage discharge defect diagnosis method in the field of transformer partial discharge partial discharge monitoring technology in an electric power system. The method comprises collecting a partial discharge pulse signal of a transformer in a signal power frequency period and extracting the number of the pulse, carrying out a statistics towards the phase distribution of the transformer discharge impulse and acquiring the phase distribution range of the pulse, detecting the content of acetylene in the transformer oil, using oil paper insulation early stage discharge defect to set a standard and determining whether the oil paper insulation discharge in the transformer is at an early stage or not. According to the invention, a goal of recognizing early stage partial discharge defects in the transformer is achieved by observing characteristic parameters such as the frequency and phase of the discharge impulse, the gas content in the oil and the like and supports are provided for the state assessment and maintenance of the transformer.