The invention relates to the technical field of engine idle speed control, and discloses a method for controlling a torque of an air circuit at an engine idle speed. The method for controlling the torque of the air circuit at the engine idle speed comprises the following steps that: S1, whether idle speed closed-loop control is activated or not is determined, if yes, step S2 is executed, and if not, a torque of the air circuit at an idle speed is not requested; S2, a moment of inertia J in the idle speed closed-loop control is obtained according to an initial value J<Engine> of the moment of inertia and a fixed change rate [delta]J<CreepDelta> of the moment of inertia of an engine, and a reserve torque time constant lambada is determined according to f and k; S3, a P term parameter, a D term parameter and a I term parameter of PID control are calculated and obtained according to lambada, an air intake system time constant [Tau]<Air> and J; S4, a P term torque M, a D term torque M<D>and a I term torque M of an air circuit reserve torque are calculated according to the P term parameter, the D term parameter and the I term parameter; and S5, according to M, M<D>, and M, the torque M<AirFinal> of the air circuit at the idle speed is calculated. The problem that conventional PID control is used when controlling the torque of the air circuit in the prior art is solved, and the problem that the conventional PID control has many control parameters, complicated calibrations, and has a lot of calibration work that a calibration engineer needs to do is solved.