The real-time measurement of welding temperature field by colorimetric method is described, and with the data acquired from it closed-loop control system of the parameters of temperature field is developed and tested. Experimental results prove that it has high measurement speed (time of a field within 0.5s) and good dynamic response quality. Weld penetration can be controlled satisfactorily under unstable welding condition. The real-time measurement of welding temperature field by colorimetric method is described, and with the data acquired from it closed-loop control system of the parameters of temperature field is developed and tested. Experimental results prove that it has high measurement speed (time of a field within 0.5s) and good dynamic response quality. Weld penetration can be controlled satisfactorily under unstable welding condition.