Abstract: In view of the defects of the existing series-connected oil-electric hybrid heavy truck’s long downhill braking system, a power battery state of charge（SOC） control strategy based on exhaust brake of hybrid heavy trucks was proposed. Different SOC thresholds were set according to the characteristics of lithium batteries. The electric characteristics of the generator in its vehicle-mounted generator set were used to drive the engine to operate. The exhaust brakes were used to consume their feedback braking power and excess power to ensure that feedback braking was operated effectively for a long time, avoiding the risk of degraded braking performance and overcharging of power batteries in long downhill conditions, thereby improving driving safety. MATLAB/Simulink simulation analysis and bench test verification results show that the strategy can ensure that feedback braking is effective for a long time, reduce the frequency of mechanical braking and the operating strength, and is conducive to driving safety. It can realize dynamic adjustment of battery power, effectively avoid overcharging the power battery, and extend the life of the power battery. And it can ensure that the matching error between feedback braking power and power consumption is within ±5%.