Computer simulation on heat treatment is the foundation of intelligent heat treatment. The simulation of temperature field, phase transformation, stress/strain in complicate quenching operation has been realized with the three dimensional non-linear finite element method model and the methods of treating for abruptly changed interface conditions. The simulation results basically fit those measured in experiments. A production line with intelligent sealed multipurpose furnace has been developed based on the combination of computer simulation on gaseous carburizing and computer control technology. More than 3 000 batches of workpieces have been processed, and all are up to standard. The application of computer simulation technology can significantly improve the load-carrying ability and reliability of the nitriding and carburizing workpieces, reduce heat treatment distortion, and shorten carburizing duration. It is recommended that the reliable product design without redundancy be performed with the combination between the CAD of mechanical products, the CAE of materials selection and heat treatment, and the dynamic evaluation technology of product reliability.