Abstract:A new method for 3D-circle testing was presented.In the method,all observed points are fitted to a plane,and the sphere can be fitted by mid vertical planes,which are composed of the space vector,the 3Dcircle center locates in the fitted plane.The coordinates of the center and the radius can be calculated by the method directly.The gross error will be eliminated during the fitting process.Compared with other methods,the method is very easy to realize,and reliability and fitting precision are higher.