Abstract: In order to design more reasonable fiber combining resonator, Fourier optical theory is used to analyze the self-imaging resonator, and the selection method of three key components, including Fourier lens, filter and output mirror, is discussed.Particularly, the paper used MATLAB for numerical simulation and obtained a method of calculation for space filter transmittance function.Then two circular light fields with radius of 55 mm were taken as an example, the distance between the both was 240 mm, and the amplitude and phase distribution of spectrum plane after Fourier transform was simulated.The same-phase distribution of two light fields is obtained by comparing phase.At the same time, the paper analyzed the cavity according to transfer matrix theory, and obtained both the necessary conditions for stable oscillation of self-imaging passive cavity, and the conditions for highest fiber coupling efficiency of oscillating light.