Aiming at planar linkage mechanisms considering joint clearance effects, a modular approach based on the link group theory and the graph theory is proposed to improve modeling efficiency. The massless link model to simulate joint clearances provides possibility for using modular approach to analyze the clearance effects. Meanwhile, this approach highlights the hierarchy and reusability of a defined mechanism when solving similar cases. A revolute four-bar mechanism with joint clearances is studied as a case to demonstrate the effectiveness of the proposed approach. This approach is an efficient mechanism analysis method on account of clearance effects and can improve the modeling efficiency significantly.