Based on the fuzzy theory and an idea of multidisciplinary design optimization, a fuzzy optimization model of multidisciplinary design is established. Fuzzy constraints are changed by a fuzzy comprehensive evaluation and an amplification-coefficient method. Using collaborative optimization and genetic algorithms, the multidisciplinary fuzzy optimum of planar linkage mechanism is achieved and a four-bar mechanism is given as an example. Two disciplines are involved in the design optimization of mechanism, i.e., kinematics and control. The numerical results indicate that the optimized mechanism not only satisfies the mechanism and control constraints, but also synthesizes approximate optimum value, and lays a foundation for the solution of more complex mechanical system.