The paper attempts to analyze Chinese trade union’ coverage effect on the wage gap by adopting the method of Blinder-Oaxaca，based on employees and employer matching data in 2012. The results show that under the unions membership effect，Union status have no significant impact on wage；The union status affects on wage by changing the returns of labor contract；Union identity affect the level of wages through collective contract signing rate；Union identity affects the salary level by increasing return on human capital；Union membership tendency is a kind of system；The union identity can reduce wage discrimination.