The invention provides a welding robot device for welding of a plunger pump power end shell. The welding robot device for welding of the plunger pump power end shell comprises a controlling system, a portal frame X-Y-Z coordinate system, a welding system, a space positioner and a tool clamp. The tool clamp is used for clamping the plunger pump power end shell, and a plunger pump shell can be one-time clamped; all welding joints of the plunger pump shell can be positionally changed to a flat welding position or a flat fillet welding position through the space positioner; a welding mechanical arm is connected with a coordinate Z-axis in the portal frame X-Y-Z coordinate system, and welding of welding joints in the different positions can be finished; and synchronized driving of the welding mechanical arm, a coordinate X-axis, a coordinate Y-axis, the coordinate Z-axis and the space positioner can be realized, so that continuity during the welding process is guaranteed, and welding quality and welding efficiency are ensured.