In this paper, based on the experimental measured cooling curves, it was solved that the inverse problem of non-linear heat conduct equation for Steel 1045 quenched by water using finite difference method and nonlinear estimate method. The volume fraction of constituent of austenite, pearlite, bainite, martensite and the non-linear surface heat-transfer coefficients in continuous cooling during quenching were calculated and simulated by mathematical transformation. The volume fraction of phase constituents in the quenched work piece of 1045 steel was tested subsequently. Then the temperature field and thermal stress field of Steel 1045 cylinder during water quenching was simulated by ANSYS. The study results show that the 2D transient temperature field of the cylinder specimen calculated by ANSYS during quenching coincides with the practical quenching process, and the results of thermal stress field simulated by ANSYS can guide quenching process.