The invention relates to a gear pump and a bypass oil path structure thereof. The bypass oil path structure comprises a drainage cover and an overflow adjusting valve arranged on the drainage cover. The drainage cover comprises a bottom plate and a side wall extending in the axial direction from the peripheral edge of the bottom plate. A drainage hole is formed in the bottom plate. An overflow hole is formed in the side wall. An installing part is further arranged on the drainage cover. The installing part is close to the drainage port, and part of the installing part is formed in the side wall of the drainage cover. The protruding extending direction of the installing part skews relative to the radial direction of the drainage cover. A bypass hole is formed in the installing part in the protruding extending direction of the installing part in a penetrating manner. The bypass hole communicates with the drainage port of the drainage cover and the overflow hole. The overflow adjusting valve is movably arranged in the bypass hole and used for disconnecting the bypass hole and the drainage port. The bypass oil path structure is compact.