According to the function requirements of CAD system of heat transfer equipment design in thermodynamic fields, data contained in a CAD system and its subsystems of shell-and-tube heat exchanger were analyzed synthetically, and the layout and design of system database were carried out. The framework of system database was presented, and the function and application of databases in the system including physical parameters, engineering materials, geometrical parameters of parts and drawings were discussed. The design and practice of database offer reference for design and application of database in other machinery CAD systems.