In the passive estimation of mobile target track, the stationary ground platform only provides angular information but no distance information. So, the target flying track must be estimated solely with the existing angular information. A new algorithm, based on uniform acceleration and constant altitude flying mode hypothesis, is presented to estimate the mobile target track according to the measured angular information. A simulation model was built to test the performance of the algorithm. The experimental results show that the estimation algorithm can reduce the angular error to milli-radian or less.