Aiming at job-shop scheduling problem with a view of minimizing the maximal makespan, an improved adaptive genetic algorithm based on hormone modulation mechanism was employed. This algorithm has such characteristics as avoiding inbreeding efficiently, no needing reproductive operation, overcoming premature phenomenon and slow evolution. An operation-based code was applied to job-shop scheduling problems along with the satisfied results. Numerical simulation demonstrated that within the framework of the newly designed improved adaptive genetic algorithm based on hormone modulation mechanism, the needed time for new optimal scheduling project and the minimal makespan were decreased, therefore the NP-hard job-shop scheduling problem can be solved efficiently.