A new 3-DOF parallel Coordinate Measuring Machine was proposed in this paper, which could realize 3D measured with only one linear grating and one precision guide. A kind of calibration method based on the distance of two points is proposed. In the scheme gauge block is utilized as benchmark, Gauss-Newton method, a non-linear least square computational method, is used to solve the measuring equation of the CMM, to get the precise parameter of the machine. Experimental results show that this method can effectively improve the over-all accuracy of the 3-PSS CMM. The further study is in process, we will identify the actual values of input parameter errors and mechanical errors in the software compensation.