Abstract: The characteristics of a trans-lunar trajectory affected by some parameters such as the height of perigee, trans-time and inclination of transfer trajectory is analyzed in this article. Assuming a lunar explorer is injected into the transfer trajectory from a circle earth parking orbit on 025000, 08/27/2004 and approaches perilune of 200km high forming a polar lunar orbit. Two velocity impulse at perigee and perilune are calculated. The results show that the inclination of transfer trajectory has little effect on the velocity impulse of perigee, but remarkable on the velocity impulse of perilune. A transfer trajectory with certain inclination should be chosen to the least fuel consume. The total velocity impulse will decrease with the trans-time increases. When the trans-time is longer than 90 h, the total velocity impulse varies little. But the trans-time of 120h is chosen to ensure that the spacecraft be observed at perilune. The fuel can be saved by increasing the injecting height, but the capability of launch vehicle should be considered simultaneously to decide the height.