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.