The invention provides a brushless direct current motor which comprises a stator with pairs of stator teeth, a rotor with pairs of magnetic poles, and a rotating shaft fixed at a rotor center hole. Each stator tooth coils a winding, in each cross section of the stator, an intersection point of an tooth top arc line of each stator tooth and a tooth shaft radius of the stator tooth is connected with a center of the tooth top arc line of each stator tooth, and a mechanical eccentric angle which is larger than 0 degree and less than 90 degrees is formed between the tooth top arc line of each stator tooth and the tooth shaft radius of the stator tooth. Through designing a tooth top arc shape of the stator tooth as an arc line which is eccentric relative to the a rotor rotating center, such that the brushless direct current motor can eliminate a starting 'dead point', and starting is smooth; current drive with a sinusoidal rule change can be matched, thus an air gap magnetic field uniformlychanges with a sinusoidal rule, torque fluctuation is reduced, and vibration noise is reduced.