To meet the requirement of online measurement of large forgings in thermal state, a method based on structured light stereo vision technique was presented. To solve the problem of the acquirement of structured light strip on the condition of thermal state, the method combined physical filtering and digital filtering to overcome the influence of red thermal radiation，and temporal phase unwrapping structured light technology was also used to improve the optical noise immunity significantly. Multi-view auto registration techniques based on mark balls were adopted to measure large objects. An experimental system has achieved non-contacting 3D measurement of large forging in 15 m distance. The experiment proves that the method has advantage of high-speed and high- precision, and it is also simple and convenient,which can meet the requirements of online measurement of large forging in thermal state.