The correct detection of phase current was the premise to realize torque control in brushless DC motor (BLDCM) direct torque control system. The relationship between electromagnetic torque and phase current of BLDCM was studied. The hardware circuit and software algorithm of phase current detection were designed. The phase current was detected by Hall current sensor and transferred to the AD conversion module of DSP through conditioning circuit. For the offset and gain error caused by AD conversion, the least square method and linear fitting function were used to correct the data. Aiming at the accidental error caused by individual data, a current composite filtering method was proposed. A firstorder lag filter was added to the AD correction for periodic interference. The experimental results showed that the phase current detection and processing method greatly reduce the current measurement error, realized the realtime observation and direct control of torque, and effectively inhibited the torque ripple.