The invention discloses a direct-coupled air compressor driven by a brushless DC motor and a control method thereof. The direct-coupled air compressor essentially consists of a generation part of a low pressure stage, a generation part of a high pressure stage, an air reservoir part and a control system part. The generation part of a low pressure stage and the generation part of a high pressure stage are arranged symmetrically at the two ends of a main shaft of the air compressor. The generation part of a low pressure stage and the generation part of a high pressure stage are connected by a copper pipe; the generation part of a high pressure stage is connected with the air reservoir part by a copper pipe; motor shafts of the motor and the control system part and the main shaft of the air compressor are coaxial. The direct-coupled air compressor driven by the brushless DC motor of the invention has high efficiency, light weight, small volume, portability and low production cost. The control method of the invention skips the measurement of the rotating angle and rotating speed of the motor, omits common PI control, can cause the rotating speed of the motor to be more stable when greatly simplifying the control system and lowering cost, thereby further improving the efficiency of the motor and reducing noise caused by the fluctuation of the rotating speed.