Abstract: To improve the inefficiency of the immune algorithm in solving combinatorial optimization problems including job shop scheduling problems,this paper adopts the multi-clone operator and a unique density-control scheme to improve the immune algorithm’s optimizing ability.The multi-clone operator is introduced from the genetic algorithm to widen the searching space of the problem,and the density-control scheme is enlightened by the concept "niche" in biology,which can lower similar individual group’s propagation probability among the population to avoid local trap in searching.The algorithm is designed for job shop scheduling problems,whose effect is validated by a series of job-shop scheduling benchmark problems.