Combined with the low temperature material properties accurately obtained by the experimental test and the boiling heat transfer coefficient of specimen immersed in the liquid nitrogen bath acquired by an empirical formula method, a numerical model based on metallo-thermo-mechanical couple theory is established to reproduce the deep cryogenic treatment (DCT) process of a commercial newly developed cold work die steel Cr8Mo2SiV (SDC99) considering phase transformation and its latent heat effects.Moreover, an experimental setup for rapid temperature measurement is designed to validate the simulation results.The investigation suggests that the cooling behavior at various points of the solidified specimen show the similar trend, but the differences in temperature and cooling rate between the surface and core of specimen is still very significant.However, it should be emphasized that the acute temperature and cooling rate changes during DCT are mainly concentrated on the specimen surface region about 1/3 of the sample thickness.Subjected to DCT, although the retained austenite of quenching specimen will continue to transform to martensite, this phase transformation is incomplete and finally its phase volume fraction is reduce to 2.3%.The predicted results are coincidence well with the experimental data obtained from the X-ray diffraction.It demonstrates that the metallo-thermo-mechanical coupling numerical model employed in this study can accurately capture the variation characteristics of temperature and microstructure fields during DCT and provide a theoretical guidance for making the more efficient and reasonable DCT procedure.