A CAD system model on the optimization of machine-tool spindle including mechanics model analysis, optimization method and drawing creation is proposed. It can create mechanics analysis model, optimization model, layout drawing with friendly interface automatically, embodied the thinking of agent design. The optimization result and final drawing can be got in hard-copy. In addition the concept of product design model is proposed. Based on OOP technology, the whole system is implemented with Visual Basic program mainly. The task of product design can be done easily by CAD system, in the same time; the result of optimization can be output or saved in document. Good result can be gotten for optimization of primary spindle in precision machined tools.