The current studies on optimal rendezvous trajectories for exploring asteroids always concentrate on the fuel-optimal two-impulse rendezvous, while the aim of this paper is aimed to investigate the multi-objective optimization problem of multiple-impulse rendezvous for exploring asteroids. A multiple-impulse rendezvous optimization model using Lambert algorithm for exploring asteroids including earth departure and heliocentric transfer phases was established, which utilized minimum-fuel cost and minimum-time transfer as two objective functions. The NSGA-II algorithm, a very representative multi-objective evolutionary algorithm, was employed to obtain the Pareto solution set. The effectiveness of the proposed optimization model and algorithm was testified by solving two asteroids mission design problems. The results show that the proposed method can effectively and efficiently demonstrate the relations among the mission characteristic parameters such as launch time, transfer time and total fuel cost, and analyze the influences of different impulse numbers, and also compare and evaluate different exploration missions. The proposed method has good application value for preliminary mission design for asteroid exploration.