Abstract: Orbit control strategy was designed for emergency condition of Mars flyby after non-implementation of approach braking. By analyzing acceleration effect of gravity boost during Mars flyby and long-term evolution of the orbit after the flyby, the strategy design was determined from two dimensions of orbital control energy and waiting time. On this basis, several strategies were designed under the branches of energy optimization, time optimization and energy time cost compromise. Advantages and disadvantages of each strategy were quantitatively compared after theoretical analysis and simulation verification. It is concluded that energy optimization and time optimization can be the first choices. The designed emergency strategy guaranteed successful approach braking implementation under control in the first Mars exploration missions of China. Research methods and conclusions can provide technical support and quantitative reference for flight control decisions and emergency control, and can be extended to other planetary exploration missions with similar background.