In order to improve the accuracy of tooth profile deviation in machine,a method which can get the radial error based on the actual working condition is proposed. According to the principle of polar coordinates measuring and tooth profile deviation calculation,an optimization model with purpose of minimum tooth profile and variable parameter of radial error is established based on the object of standard involute spur gear.After resolving this radial error and compensating the machine with the error,a helical involute gear is measured and the measured result is compared with the testing result of the three coordinate of the testing results of the three coordinate measuring instrument,the rationality of the radial error solving of the measuring head is obtained.