For the high need of direction aiming at ultrasonic testing, especially the test of surface work-pieces, it is necessary to make error compensation to improve the test accuracy. The kinematics analysis of ultrasonic robot was firstly done, then the principle and compensation model of multi-joint error compensation was expatiated though the analysis of sources and traits of the pose error. Finally the example was given to validate the error compensation method, by which the continuous ultrasonic test for curve surface was realized by exact control parameters. 