Aiming at the defect of loss of ripple information in the modeling of the traditional state space averaging method, based on the linear time period theory and harmonic linearization theory, the Fourier decomposition method is used to establish harmonics under steady-state operation of DC/DC converter State space model, draw the harmonic equivalent circuit of DC/DC converter, describe the mapping process of topological current and voltage from the frequency domain perspective; add a small disturbance on the input side to establish a small harmonic state space disturbance of the DC/DC converter Describe the matrix and analyze the steady-state harmonics and disturbance interharmonics. Simulation and experimental results show that the DC/DC circuit modeling method based on the harmonic state space has high accuracy and has certain engineering application value in the harmonic analysis of distribution scenarios in future with multiple converters.