The invention discloses a piezoelectric resonator. The piezoelectric resonator is characterized by comprising a metal base, and a shell arranged on the metal base; the shell and the metal base form asealed cavity; the piezoelectric resonator further comprises a piezoelectric wafer; the upper and lower surfaces of the piezoelectric wafer are respectively plated with a metal electrode layer; the piezoelectric wafer is arranged in the sealed cavity, fixed on the metal base and electrically connected with the metal base; a filling gas is filled in the sealed cavity; the shell is configured with athrough hole; and the through hole is filled with an elastic sealing element. The invention further discloses an air pressure monitor including the piezoelectric resonator, and an air pressure monitoring method using the air pressure monitor. The piezoelectric resonator of the invention transforms a pressure signal into the precise frequency change through the transfer of the air pressure by elastic materials, so as to accurately measure the air pressure. According to the air pressure monitor provided by the invention, on the one hand, the piezoelectric resonator is adopted, so that the induction of the air pressure is accurate; and on the other hand, a signal converter and an alarm are combined, so that real-time monitoring and early warning are realized.