The invention discloses an anaesthesia machine and an APL valve thereof. The anaesthesia machine comprises a breathing circuit, a fresh gas branch, a manual driving gas branch, a discharge branch and the APL valve, and the APL valve is installed on the manual driving gas branch to limit the gas pressure in the manual driving gas branch. The APL valve comprises a valve seat assembly, a pressure adjusting assembly, a valve plate assembly and an elastic piece; the valve seat assembly is provided with an gas inlet and an gas outlet, the gas inlet is communicated with the manual driving gas branch, the gas outlet is communicated with the discharging branch, and the pressure adjusting assembly is movably installed on the valve seat assembly. The valve plate assembly is in sliding connection with the pressure adjusting assembly, an gas cavity is defined by the valve plate assembly and the pressure adjusting assembly, the valve plate assembly is used for controlling connection and disconnection between the gas inlet and the gas outlet, the elastic piece is arranged in the gas cavity, the first end of the elastic piece abuts against the pressure adjusting assembly, the second end of the elastic piece abuts against the valve plate assembly, and the APL valve is further provided with a damping hole communicating the gas cavity with the outside. The damping hole is used for discharging and sucking gas in the gas cavity so as to restrain resonance of the valve plate assembly.