By using an infrared temperature measurement technology and combining conduction with convection, a method to reversely calculate the solidification temperature of a casting part according to its surface temperature measured in the casting process is proposed. It is verified that the method can give a more accurate quantitative detection result from the surface temperature of the casting part in its casting process. The actual test result shows that this method is feasible. In addition, it can reversely calculate the surface temperature of different casting parts during casting by writing a simple program and inputting the specific parameters of different parts. So, this method can be used in the production of casting.