The invention relates to an underwater natural gas pipeline connector leakage monitoring system which is characterized in that a plurality of underwater sensing subsystems and an on-water monitoring device are included, each underwater sensing subsystem comprises an external frame, each external frame is provided with a plurality of hydrophones and an electronic bin, a signal pre-amplifying plate, a data collecting plate, a USB data collecting card and a first optical fiber transceiver are connected in sequence in each electronic bin, the on-water monitoring device comprises an industrial personal computer and a plurality of second optical fiber transceivers which are connected with the first optical fiber transceivers through optical cables in a one-to-one-corresponding mode, the industrial personal computer is provided with an operation displaying interface, and the industrial personal computer displays the alarming signal and the leakage position of a hydrophone at each position through the operation displaying interface of the industrial personal computer. The underwater natural gas pipeline connector leakage monitoring system can be widely used in the field of underwater natural gas pipeline connector leakage.