The invention relates to a piezoelectric flexible diaphragm pump which comprises a piezoelectric ceramic, a vibration substrate, a liquid storage cavity, a driving hole, a driving liquid, a flexible diaphragm, a pump cavity, an inlet check valve, an outlet check valve, an inlet and an outlet, wherein the piezoelectric ceramic and the vibration substrate are bonded to form a piezoelectric vibrator; the piezoelectric vibrator is arranged at the upper part or the lower part of the liquid storage cavity; the driving hole communicated with the liquid storage cavity is formed in the upper part or the lower part of the liquid storage cavity; the flexible diaphragm is arranged at the driving hole and separates the driving liquid from the pump cavity; the piezoelectric vibrator, the liquid storage cavity and the flexible diaphragm jointly form sealed space, and the space is filled with the driving liquid; and the inlet check valve and the outlet check valve are mounted at the inlet and the outlet of the pump cavity respectively. According to the piezoelectric flexible diaphragm pump, the flexible diaphragm is indirectly driven to move by liquid power, so that the overall deformation of the piezoelectric vibrator can be fully used, and a high pump cavity compression ratio can be realized; and the piezoelectric flexible diaphragm pump has the advantages of good self-sucking performance and high bubble discharge performance and output pressure.