The invention discloses an elliptic-circular compound cycloid rotor oil pump, a rotor thereof and a rotor design method. The elliptic-circular compound cycloid rotor oil pump comprises an inner rotor and and outer rotor which are engaged to each other, the tooth number of the outer rotor is 1 less than that of the inner rotor, the tooth profile of each tooth of the outer rotor is composed of an elliptic arc and a circular arc tangential to the elliptic arc, the elliptic arc length is the distance between the tooth peak A and the elliptic-circular compound point F, and the circular arc length is the distance between the elliptic-circular compound point F and the tooth bottom; the tooth profile of each tooth of the inner rotor is the conjugate curve of the tooth profile of the outer rotor, and the inner rotor and outer rotor are engaged in a single-tooth mode. The oil pump rotor design method overcomes the problem of large tooth profile sliding at the engaging boundary point and also solves the problem of easiness in engaging impact generation due to the fact that only one part of the tooth profile sections of the outer rotor of the current elliptic cycloid rotor oil pump participates in engaging; the elliptic-circular compound cycloid rotor oil pump has advantages of small engaging abrasion between the inner rotor and outer rotor, good sealing property and high oil pump volume efficiency.