In order to solve the accurate test problem of encoder angle error with limited angle , the angle error of encoder is tested by plane mirror-autocollimation theodolite. The mathematical model of the relationship between the angle error, the pose dislocation parameters, the angle of encoder and the value of the theodolite is established, the system error of the encoder angle can be corrected by calculating the pose dislocation parameters. The experimental results show that the angle error introduced by the pose dislocation increases monotonically with the increase of encoder angle when the angle range is 0°~40°, the maximum angle error is 742.9". The corrected angle error is basically the same as the angle error without encoder pose dislocation, the maximum angle errors are 4.4" and 3.5", respectively. Encoder angle error with limited angle that cannot be accurately adjusted or does not have a leveling condition can be effectively evaluated by this method.