Abstract: In this paper, 45 steel friction welded joint is tested by using 15MHz ultrasonic focused transducer and a arithmetic model to calculate the residual stress in the friction welded joint through ultrasonic testing is established based on the theory of the finite elastic distortion. In addition the distribution laws of axial and radial stressure in the joint are worked out, The results show that the axial stress is press are stress in the weld and nearby area but is pull stress in the far area apart from the weld. The radial stress is press stress in the joint axis and is gradually from press stress change into pull stress in the area further away from the axis. The experiment results also show that the material anisotropy has important influence on the ultrasonic technique of measuring the residual stress in the friction welded joint. The axial stress distribution law which is got by ultrasonic technique is closing to the law worked out based on the theory of finite element. Besides, the arithmetic model proposed in this paper will decrease the residual stress error, and the method is more accurate than the finite element method in measuring the residual stress in the friction welded joint.