The invention discloses a diaphragm compressor and a flow regulating method thereof. The diaphragm compressor comprises a cylinder component comprising a diaphragm, a hydraulic cylinder, a cover plateand a support plate, wherein the periphery of the diaphragm is fastened between the cover plate and the support plate to form a membrane chamber and oil chamber; the support plate and the diaphragm enclose a hydraulic cylinder; a crankcase, wherein the upper case of the crankcase is connected with a cylinder component; a gear pump, which is arranged on one side of the crankcase and connected witha lower tank body of the crankcase through an oil suction pipe; and at least one plunger pump, which is disposed outside the gear pump and connected with the gear pump through an oil passage. The oiloutlet of the plunger pump is connected to the hydraulic cylinder through an oil replenishing pipeline to supplement oil for the oil chamber. Stepless adjustment of the gas flow rate of the diaphragmcompressor during the operation of a machine can be realized by adjusting the oil replenishing time of the plunger pump, thereby solving the problem of insufficient air suction at the time of oil replenishing of an existing diaphragm compressor. The diaphragm compressor is more convenient and economical, and energy consumption is also reduced.