This paper presents an optimal method of aiming for an approximately straight path of the Modified Watt’s Linkage (MWL) within limited dimension. A modification to the Watt’s linkage and the corresponding condition are introduced, followed by the kinematic synthesis. The path generation based on the modification considering constraints from practical application is provided. Genetic algorithm is utilized to perform the constrained optimization. The centrosymmetric property of the MWL is considered in the synthesis process. Ideal parameters of the mechanism are achieved to demonstrate the effectiveness of the proposed method.