The heat transfer process of medium carbon steel laser quenching has complex unsteady heat transfer characteristics, which are difficult to be accurately described by adopting traditional heat conduction models. The unsteady heat transfer control equation of medium carbon steel laser quenching considering the above influences is deduced, the heat conduction and temperature field variation laws of this process are explored, and a simulation model of unsteady heat transfer characteristics of medium carbon steel laser quenching is established. A laser quenching test system for medium carbon steel and measuring the temperature data during the actual quenching process is established to verify the reliability of the simulation method. The prosed heat source model for laser quenching on 45 steel surface has been proved to be effective by comparing the simulation results with the test ones.