The invention discloses a control method of a small machine direct exhausting and large machine air cooling system of a supercritical thermal power generating unit. The control method comprises a unit coordinated control system instruction generation and generation loop unit and a water feeding system feedforward control loop, wherein a load instruction generation and lifting load speed generation loop includes a cutting AGC loop unit and a steam condenser vacuum RB loop unit. The control system solves such problems as high fluctuation of a water feeding system along with the back pressure change, weak unit stability and non-planed stop risk in a supercritical small machine direct exhausting and large machine air cooling unit, respectively adopts different control loops and conversion functions under different working conditions to realize following-up of the target load and lifting load speed of a unit coordinated control system, adopts feedforward polygonal functions to realize rationality of feedforward amplitudes of the water feeding system, guarantees the fastness and the accuracy of the unit water feeding system, and guarantees the operation safety and stability of the unit.