The problem of the robustness design of path generating mechanism was discussed with fuzzy mathematics method in this paper. Then the principle of fuzzy robust design and the mathematical modeling method were put forward. With a four-bar path generator taken as an example

the fuzzy robust optimal design was accomplished. The method is able to control the movement error in design principle and the stochastic movement error caused by the manufacture error

and also can make the movement precision of mechanism match up to the tolerance of each dimension in reason. The principle put forward in this paper provides a new rational method for the path generating mechanism

so it possesses biggish value in engineering application.