The invention discloses a method for damping control of an LCL grid-connected inverter based on dimension reduction observation. The method includes the steps that a single-phase system differential equation of a grid-connected LCL filter is established; the system equation is decomposed into a subsystem without reconstruction and a subsystem needing reconstruction; a characteristic polynomial for the reconstruction subsystem is solved; a dimension reduction observer for the reconstruction subsystem is designed; a characteristic equation of the dimension reduction observer is solved. According to the method for damping control, a sensor for sampling capacitor voltages or capacitor currents in a traditional control method is omitted, the capacitor currents are observed through feed-forward, and then system resonance is restrained and system reliability is improved.