Aiming at the damaged blades of hydraulic turbines or other structures with spatial complicated curved surfaces，which can be repaired directly in their installation position, an virtual prototype of the welding robot based on the mobile platform was designed. In order to determine the kinematic relationship between end of the welding torch and all robot joints, the DH coordinate system of the virtual prototype was built up, then the forward kinematics and inverse kinematics were obtained with Matlab software.The threedimensional (3D) model of the welding robot was imported into ADAMS simulation software, which was set up with SolidWorks software, then the kinematics analysis was done. The simulation results show that space displacement changed little caused by the plane joint and rotational joint, velocity and accelerationcurves changed smoothly without any mutation which can prove the effectiveness of the virtual prototype design, and satisfy the needs of the welding work inside of foundation pits.