To improve the location accuracy of two-dimensional stage, a profile online detection method for two-dimensional stage x axis mirror is proposed. Without the y axis mirror, the quadratic differential information of the stage x axis mirror is detected by the three-path laser interferometer. The quadratic integral is conducted for the obtained data to obtain the accurate profile of stage mirror. The influence of zero error on the profile deviation detection for stage mirror is analyzed and a corresponding calibration scheme is proposed. Theoretical analysis and experimental verification are conducted for the proposed method. The results show that the accuracy of detection repeatability is better than 2.6521 nm by the proposed method, the correctness of the profile deviation detection for stage mirror is verified, and the real-time compensation for the profile deviation of the stage x axis mirror is achieved.