Abstract: The invention develops a computer-aided drug design method and system to optimize a lead through structure-based drug design with synthetic accessibility. In this invention, two systems of the structure-based lead optimization are developed and implemented: 1) LeadOp (“short for lead optimization”)—an algorithm that performs lead optimization through structure-based fragment hopping method; and 2) LeadOp+R (short for “lead optimization with synthetic accessibility based on chemical reaction route”)—an algorithm that performs lead optimization with synthetic accessibility. LeadOp algorithm provides users to optimize a lead compound with various combinations of fragments with stronger binding based on group efficiency, generating lead with stronger potency. Furthermore, LeadOp+R provides an advantage in the selection of the new fragment to be assembled, which was identified based on the group efficiency calculated in the active site and reaction rule.