A synchronous on line precision detection method for threedimensional angles (yaw, roll, pitch) is proposed in this study based on the measurement results of standard stepgauge block parameters, which is employed for the fast detection of motion angle errors in linear motion system. The system uses a line laser sensor to achieve the real time acquisition of the stepgauge block parameters. And the mathematical model of the stepgauge block parameters and its threedimensional angles is established. The system measurement stability and repeatability are verified with the calibrated precision turntable. The measured values are compared with the theoretical values, it is determined that within the measurement range of ±30°, the measurement error is less than 1%. The experiment and software calculation combined method was adopted to determine the angle measurement resolution, the result shows that after calibration the angle resolution is 0001°. Finally, the proposed system was used to implement the simultaneous measurement of the three motion angle errors of the zaxis in a threedimensional moving platform, the measurement result verifies that the proposed system possesses the characteristics of simplicity, practicability and high efficiency.