Abstract: As the systematic error of the optoelectronic theodolite, the orientation error of the azimuth shafting encoder can be numbered and corrected before measuring. But the orientation error, as the systematic error, can constantly vary randomly in the course of work and inevitably make great influence on the measuring accuracy. It is believed that the gap between the joint lever and the switch port, when the leveling gear and the foundation bed are attached to each other, is the cause of error varying. On the basis of analyzing the previous solutions, the mechanical construction model combining the leveling gear and anti-twisting thin film was proposed, and it was found out that within the range of angle 7', both the bending stress and shearing stress of anti-twisting thin film were admissible stresses between the internal circle and the external circle of the anti-twisting thin film. The corner was smaller than 1of the encoder in precision. Thus the problem of azimuth axis angular adjustment was solved and it was assured that no orientation error occurs when it is under the moment of 4 000 Nm. Practice has shown that the approach is effective in solving the orientation error varying.