Grind-hardening is a new integrated machining technology which utilizes grinding heat to quench the non-quenched steel directly. In this paper, the technology is applied in the process of rack form grinding. A comprehensive numerical model is developed to simulate the temperature distributions of the rack under the dry grind-hardening conditions with finite element method(FEM). The temperature dependency of the thermal properties, the triangular heat distribution of the heat flux, latent heat and the air convection are taken into account. The simulated hardness penetration depth(HPD) is deduced from the local temperature distribution, time history of workpiece according to martensitic phase transformation theory. This provides a reliable method for the proper selection of process parameters in order to produce enough heat at the contact zone, enabling the treatment of the rack.