A new method,the concurrent optimal design for the mechanical product accuracy is addressed presented, this method is very suitable to a concurrent engineering context. Differing from the convensional tolerance design method, this method establishes a direct link between product working accuracy and machining precision of the parts. Therefore, in the product design phase,the optimal machining tolerances which satisfy the product working accuracy can be determined. Using this method, the design and manufacturing time and cost can be enormously reduced and product quality can be guaranteed.