In order to improve the charge efficiency of Baja racing engine,enhance the performance of the engine,and take into account the safety,the intake system of Baja racing car was designed.Firstly,the di-ameter and length of the intake pipe were calculated according to the fluctuation effect.Then the engine model was established in GT-Power software according to the original engine parameters,and a plenum was added.The effects of cavity's diameter on engine's output power were compared to select the best one.Finally,the intake pipe waterproof part is designed to make the car have better waterproof perfor-mance to face the harsh environment of the off-road track.