Abstract: Colormetric method by using two different wavelength images is a new measuring method for temperature field on the basis of ordinary colorimetric method,which depend little on the measuring distance,emissivity of body etc.In this paper the real-time measuring system and measuring principle of welding temperature field by the method are described,the whole welding temperature field is real-time measured,so the temperature distribution at the welding direction and its section is obtianed,then parameters of thermal cycle.With data from the temperature close loop control system of the parameters of temperature field is developed and tested.Experimental results prove that it has high measuring speed (less than 0.5 s/field) and good dynamic response quality.Weld penetration can be controlled satisfactorily under regurous welding condition such as welding thickness variation,welding speed variation and weldment gauge variation etc.