In order to reveal the friction and wear characteristics of large gears used for wind power and hydraulic ship and avoid the occurrence of early catastrophic failures, the wear characteristics and evolution process of helical gears under linear initial defect were studied experimentally. The control variable method was adopted to process the linear initial defect along the tooth width direction by means of EDM cutting.In order to speed up the experimental process, the tooth width of the experimental gear was 1/3 of that of the standard gear. In the experiment process, the power closed current loading method was used to apply a constant load of high torque, particle counter and analytical iron spectrometer were used to analyze the abrasive particles in the oil sample, and the wear condition of tooth surface was observed and analyzed by using scanning electron microscope. The results show that the linear initial defect can accelerate gear wear, lead to the gear entering the fatigue wear stage in advance, and cause serious damage to the tooth surface, resulting in large size of abrasive particles; the oil sludge produced by gear meshing aggravates the flaw and generates to the failure of the gear.