Abstract: To analyze the accuracy and effectiveness of using SGP4 model for orbit prediction and collision alert, the space object collision alert software was made to realize it. For the three space collisions that ever happened, the space objects' position and speed were calculated to get the collision probability, using the TLEs which NORAD announced 1, 3, 5, 7 and 10 days before the collision, and then analyzed the accuracy and effectiveness of SGP4 model. The results show that, the alert collision time calculated using SGP4 model for orbit prediction and collision alert is consistent with the actual collision time, and the collision probability gets the alert warning. However, the accuracy and effectiveness of SGP4 model decrease with the increase of the alert days, and SGP4 model works best when the alert day is less than 5.