To achieve the manned asteroid exploration, the design and optimization method of two-impulse round-trip transfer trajectory for manned asteroid exploration is presented in the strict time constraint. According to the characteristics of the manned asteroid exploration, the scheme of the two-impulse transfer trajectory is established. Then the two-impulse round-trip transfer trajectory is designed preliminarily on the basis of the scheme. In each stage of the transfer trajectory, the launch window and the reach window are optimized by the sequential quadratic programming algorithm. Finally, the optimum two-impulse round-trip transfer trajectory is obtained. The simulation results show that the design of the optimum two-impulse round-trip transfer trajectory given in this paper is able to control the single impulse within 5 km/s, which is enough to achieve the manned asteroid exploration missions for 300 days by little energy.