Abstract: This paper studies the problems of precise design of the Mars probe ballistic trajectory. A fast differential correction algorithm is given. The model of the relationship between the difference of the independent and dependent variables is formulated using the two-body equations, by which the partial derivatives matrix can easily be calculated. Using the impact parameter B as mid variables, the algorithm is designed to be a two-layer iterative procedure, which can notably reduce the times of orbit propagation computations. Taking the 2018 Mars probe opportunity as an example, the algorithm is demonstrated and verified. The result proved that, using the initial value got by the Patched-Conic approach, only 6~9 orbit propagation procedures are needed to find a precise orbit. The numerical results are verified using STK (Satellite Tool Kit).