The invention provides a method of designing an injection target point of a Mars probe with optimal fuel. The method comprises the following steps of firstly, establishing a Mars B plane and transforming a target track constraint to a target point of the B plane; secondly, getting a speed increment which is corrected in the midway by utilizing a differential correcting algorithm, figuring up an equal probability impact ellipse on the B plane according to an injection error, and selecting the injection target point on the ellipse. An injection deviation, which is artificially provided, is eliminated through correcting a cruising section in the midway, so that a selection standard is that the fuel consumed for correcting the injection target point to a final target point is minimized. A plurality of points are selected on the impact probability ellipse, the speed increment required for correcting each point is figured up, then continuous sampling and calculation are carried out near the point with the smallest speed increment, and lastly, the optimal injection target point of the fuel can be approached continuously. According to the method, the probability constraint of the upper-stage impact of the probe or a rocket on the Mars can be met, and meanwhile, the fuel consumption corrected in the midway is optimized.