The invention discloses a silicon resonant air pressure sensor based on Micro-Electro-Mechanical Systems (MEMS), the air pressure sensor mainly comprises a resonance beam membrane silicon chip, a lower cover substrate, a support substrate, a metal tube seat and a tube cap. The lower cover substrate and the resonance beam membrane silicon chip are in vacuum bonding to form a reference vacuum cavity, and the support substrate which is relatively small is fixed on the metal tube seat to isolate packaging stress and thermal stress. According to pressure difference between atmosphere to be measured and the reference vacuum cavity, axial direction stress of a clamped microstructure beam on a pressure membrane is changed, thus resonant frequency of the beam is changed, change of the resonant frequency is detected and air pressure measurement is realized. According to the invention, a resonator is placed in an air pressure medium, packaging difficulty is lowered substantially, and the packaging stress and thermal stress are isolated through cantilever supporting. The silicon resonant air pressure sensor has the advantages of simple manufacture and packaging, good stability and the like, and is suitable for high performance air pressure measurement.