The invention discloses a method and system based on jet flow for reducing noise of rotor wings. The method comprises the steps of acquiring rotor wing parameters and working parameters of a helicopter; acquiring the thickness noise characteristics of a first rotor wing at an observation point; obtaining the thickness noise characteristics of a plurality of second rotor wings at the observation point; determining an objective function, wherein the objective function is a function which maximizes the area of a noise reduction region of the observation point; determining the distribution position of applied external force according to the objective function; determining the value of the external force according to a sound field cancellation method; adopting a CFD numerical simulation methodfor determining a function relationship of the jet flow parameters and the external force; determining the jet flow parameters of the distribution position according to the function relationship of the jet flow parameters and the external force and the value of the external force; applying the jet flow to the distribution position according to the jet flow parameters to reduce the noise of the rotor wings of the helicopter. By means of the method and system, the area of the noise reduction region of the thickness noise of the rotor wings can be significantly increased, and the noise reductioneffect is improved.