In view of the problem of poor processing symmetry degree of high precision herringbone gear,an online type multi-degree of freedom gear phase detection device is designed,and the basic principle of symmetry error detection with the device is proposed. On the basis of that,the numerical control（ NC） programs for automatic checking the symmetry error is developed. Subsequently,the herringbone gear processing is realized with the application of the NC system to compensate the phase error. The herringbone gear processing experiments indicate that the online type multi-degree of freedom gear phase detection device is reasonable and reliable,and the symmetry error compensation based high precision herringbone gear processing method can steadily keep the symmetry degree within 0. 02 mm. Thus,the rationality and accuracy of the method is verified,and a new approach for high precision herringbone gear processing is provided.