A simple and practical calibration method is proposed to calibrate the articulated arm flexible CMM. Firstly, a quasi-spherical coordinate system is put forward based on DH method according to the special structure of the articulated arm flexible CMM. This calibration method is presented to determine and separate machine parameters and errors in a creative way based on multiple reversal technology. Experiments were carried out for a Faro Platinum 4ft articulated arm CMM by using a Chameleon 9159 5Q orthogonal CMM. The results prove the feasibility of the proposed method for articulated arm CMM calibration, and all parameters are separated completely. It provides a theoretical base for introducing error compensation and improves the measurement accuracy of the articulated arm CMM.