The invention discloses a three-cavity boosting air pump. The three-cavity boosting air pump comprises a main air pump body formed by stacking an upper pump body, a middle pump body and a lower pump body, wherein three piezoelectric cavities are formed in the upper pump body, the middle pump body and the lower pump body respectively and separated by four piezoelectric plates; fluid channels of the upper pump body and the lower pump body are connected with air inlets, a fluid channel of the middle pump body is connected with an air outlet, and the fluid channels of the upper pump body and the lower pump body are connected with the fluid channel of the middle pump body through communicating grooves. The upper pump body and the lower pump body suck outside air, and the middle pump body exhausts airflow; when the piezoelectric cavities of the upper pump body and the lower pump body shrink in volume and exhaust air to the communicating grooves, the piezoelectric cavity of the middle pump body expands in volume, so that the air in the communicating grooves is sucked into the fluid channel of the middle pump body in an accelerated manner, the air capacity of the middle pump body is equal to the sum of the air capacities of the upper pump body and the lower pump body, air in the middle pump body is exhausted from the air outlet after two times of pressurization, the output pressure of air is far higher than discharge pressure of a single-cavity air pressure, and the three-cavity boosting air pump has a wider application range.