The invention discloses a switch reluctance motor. By changing of top end radian of each rotor pole tooth, a variable air gap is formed between a rotor and a stator, so that inductance of the motor ischanged, a starting torque is increased, an output torque is increased, and torque ripple is reduced. By adoption of a variable air gap structure, the stator on the inner periphery comprises twenty-four stator tooth poles, the rotor on the outer periphery comprises eighteen rotor pole teeth, twenty-four winding coils include four phases A, B, C and D, every six windings in each phase are in series connection, the maximum torque of each single phase is high, each position of the maximum torque is appropriate, and torque ripple reduction and output torque increase are realized after superposition. Under a starting condition, in single-phase excitation, the peak torque is increased by 40% due to changing of an inductance performance curve; under a rated speed condition, due to air gap variability, the rotor saturation degree is decreased, the average output torque is increased by 1.4%, and the torque ripple is reduced by 38%.