To estimate the launch point of a non-cooperative ballistic vehicle more accurately, a ballistic retracing method for the boost-phase based on the Interactive Multi-Model algorithm and the Unscented Kalman Filtering algorithm is proposed in this paper, which can estimate its previous ballistic based on the measurement information of the boost-phase. Firstly, two dynamics models are built according to the flight characteristics of each sub-phases in the boost-phase, especially the angle-of-attack turning phase, which no one has paid attention to before. A ballistic retracing method based on the UKF algorithm is proposed for the case of certainty flight phase. Then for the more realistic situation where the flight phases are uncertainty at the time of measurement, a ballistic retracing method is proposed based on IMM and UKF algorithm, which combines the retracing problems of different phases to obtain the complete boost-phase ballistic of the target vehicle directly. Finally, the proposed method is validated by simulation, and the simulation results confirm the effectiveness of the proposed method and the accuracy of ballistic retracing and launch point estimate is greatly improved compared with previous ballistic retracing methods.