Abstract: With the expansion of the human's activity in exploring, utilizing the outer space, the total number of orbital space debris increases rapidly, which leads to an essential danger to the spacecrafts and astronauts in the future. Space environment protection is becoming the most important task in space navigation. In order to ensure the success of space mission, the low-orbit objects are more important. The forecast and alarm system of space debris is an important application of space object scouting around the earth. In order to avoid the collision between two objects, the orbit change of at least one of the two objects before their collision is necessary. In this paper, some analyses on the relationship between the increment of speed and variations of orbits are studied. Some strategies for orbit maneuvers are also given. At the same time, some research on the over pass durations from the ground stations is done. These works provide effective technique support for the forecast and alarm of space debris and spacecrafts.