The utility model discloses a small volume and large flow oil pump, which comprises an oil pump housing, an inner rotor, an outer rotor, an oil pump shaft, and an end cover with an inlet oil groove and an outlet oil groove. The utility model is characterized in that the inner rotor and the outer rotor are cycloid rotors, and the number of the teeth of the inner rotor and the outer rotor is respectively 4 and 5, or 3 and 4. The inlet and the outlet oil grooves of the end cover face the cavity body of the oil pump housing. The utility model has the advantage that under the condition of sufficiently big flow capacity, the volume of the oil pump is sufficiently small, which solves the problem of installing difficulty generated by that the requirement of the flow capacity is big and the space where a crank chamber is installed is limited.