The invention discloses a method for measuring the tidal volume of an anaesthetic machine, which can effectively improve the measurement accuracy of medical anaesthetic machine in measuring the tidalvolume breathed in or out by patients. The method comprises the following steps: (1) the average value measured by a flow sensor at the prior breathing-out or breathing-in stage is calculated; (2) theflow value of patients at the current breathing-out or breathing-in stage are collected; (3) the flow value of patients at the current breathing-out or breathing-in stage deducts the average value measured by the flow sensor at the prior breathing-out or breathing-in stage and the integration are accumulated in the whole breathing-out or breathing-in stage, thereby obtaining breathing-out or breathing-in tidal volume value; all factors interfering the flow measurement are compensated in real time so as to prevent the measurement results from being affected by the component, the pressure, thetemperature, atmospheric pressure and environmental temperature thus achieving the purpose of correctly measuring the breathing-out or breathing-in tidal volume, greatly improving the controllabilityof anaesthetic effect and realizing the purpose of the method.