The base-platform deformation and uneven of vehicle-borne photoelectric theodolite can lead to the theodolite angle measurement error larger than before. In order to improve the precision, the error should be corrected. With the level measurement meter, the angle of the platform and the horizontal plane can be measured. Based on the measurement results, an analytic geometry method of plane rotation changes is put forward for converting the results to the vertical axis tilt angle and azimuth tilt angle, and then the alignment error is analyzed，which is caused by the calculation method during measurement. At last，the relationships of composition error, alignment error, and the tilt of the platform are analyzed. The simulation and experimental results show that, within the vehicle leveling accuracy of 300″, the vehicle-borne theodolite comprehensive angle error is less than 16″, and the high precision measurement can be realized.