The invention discloses a method and device for detecting DC bus current through a single resistor and a motor control system. The method comprises the following steps of judging whether a PWM waveform output from a space vector pulse width modulator needs to be corrected or not in a first carrier period of every two continuous carrier periods; if so, firstly correcting the PWM waveform of the first carrier period and correcting the PWM waveform of a second carrier period of two continuous carrier periods by adopting a symmetric mode; and obtaining the DC bus current according to the two corrected PWM waveforms. Therefore, the PWM waveforms of two adjacent carrier periods are corrected by adopting the symmetric mode and current sampling is carried out according to the corrected PWM waveforms to ensure the accuracy of sampling current.