Abstract: The product model construction is a fundamental task for computer aided design (CAD) systems.A new type of environment FCADE using fuzzy knowledge base management system for recording and manipulating model construction process is firstly proposed in the paper.The product model construction process is considered as a series of model state transitions realized by modelling operations in FCADE. The process can be properly recorded with dependencies among the model operations. And then two basic functions for assisting with model construction activities, an undo function and a model maintenance function are discussed in detail.