This paper describes the pulsating torque of a three-phase induction motor due to a distorted source. Steady-state and pulsating torque can be simultaneously analyzed with consistency. The conditions of steady-state and pulsating torque，the relation between the harmonics of a source and the angular frequencies of pulsating torque have been cleared. General torques are the sum of steady-state and pulsating torques. The same harmonics of stator and rotor current make steady-state torques. Different harmonics make pulsating torques whose frequencies are the differences of stator from rotor harmonics multiplied by source angular　frequencies. In special case，fundamental makes fundamental steady-state torque alone. When stator and rotor current are assumed to consist of two kinds of harmonic in addition to the fundamental，three kinds of steady-state and pulsating torque appear. The authors propose a convenient table which can easily predict all the possible steady-state torques and the frequencies of pulsating torques from harmonics of a source. The table shows all the steady-state torques and the frequencies of pulsating torque. Finally，experimental data have clarified that the theory is right.

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