China's first lunar satellite Chang'E-1 (CE-1) was launched on Oct. 24, 2007. During its flight to the Moon, a series of maneuvers were performed to keep the satellite in the correct trajectory. Among these maneuvers, the one performed for Lunar Orbit Insertion (LOI) was the most important part since it directly decided whether the satellite could enter the mission orbit or not. Therefore, real time monitoring and estimation of the satellite's state during this stage became crucial. A system was developed for LOI monitoring using as few data as possible. This system included real time data transmission as well as real time data analysis which could provide the difference between the predicted and observed measurements in the first place, and then, most importantly, it also gives the ensuing orbit insertion conditions, i.e
., predicts probable future orbit parameters after the maneuver. The presented method was successfully applied for the LOI process in the mission phase.