The present invention provides a closed-loop volume control method of a breathing machine, comprising: firstly generating a voltage-flow velocity curve of a proportional valve of the breathing machine, and calculating a set inspiratory flow velocity of the breathing machine according to an actual volume VT and an inspiratory time T of the breathing machine； and letting an initial control voltage as a voltage corresponding to the set inspiratory flow velocity in the voltage-flow velocity curve, and time-division calculating the voltage controlling the inspiratory flow velocity by a closed-loop control algorithm within the inspiratory time until a real-time inspiratory flow velocity reaches a requirement of the set inspiratory flow velocity under the control voltage. The method of the invention possesses a feature of a high precision in controlling a flow velocity, as well as is quick in adjustment, without an overshot generated flow velocity and a misadjustment in control.
