This paper proposes a joint calibration method for a mobile manipulator based on product of exponential, to realize the unification of the pose calibration and the kinematic parameter calibration model of the manipulator between the mobile platform and the manipulator. The most used kinematic parameter calibration of robotic arms is based on the D-H parameter method, but the D-H parameter method cannot overcome the singularity problem when the adjacent joints are parallel or nearly parallel, and the modeling process is complicated and the model after modeling is poorly generalized. Therefore, this paper proposes a product of exponential based joint calibration method for the mobile manipulator, which does not cause singularity problems due to the parallelism of joint axes and has a simple modeling process. The method obtains the linearized models of the end position error, the zero position state rotational error and joint rotational error of the mobile arm by differentiating the kinematic equations of the whole system. The method establishes the relationship between the theoretical and actual values of joint spins by means of the concomitant matrix, and realizes the parameter update during the calculation of parameter identification based on the least squares method by changing the concomitant matrix. Using a high-precision laser tracker as the measurement tool, the effectiveness of the proposed method is demonstrated through experiments.