The invention discloses a small signal admittance modeling and stability analysis method of an LCL type grid-tied inverter. In light of the impact of a phase-locked loop, the invention provides an admittance model-based broadband small signal modeling method for an LCL type grid-tied inverter, aiming to solve a problem of LCL type grid-tied inverter admittance modeling cause by the impact of the phase-locked loop. The method researches the broadband admittance characteristic and analyzes the impact of the phase-locked loop, grid impedance and other parameters on the system stability in a synchronous rotating coordinate system. Results show that the system becomes unstable along with increase of the phase-locked loop bandwidth and inductance component in the grid impedance. When the system is in a stable state, the greater an active damping coefficient, the higher the phase margin of the system, which shows that the system stability is improved. The change of the inductance of the inverter has small impact on the system stability. Increase of filter capacitance and inductance of the network reduces the phase margin of the system and lowers the system stability.