Rare-earth　transition-metal　(R-T)　intermetallic　compounds　with　planar　magnetocrystalline　anisotropy　exhibit　enhanced　high-frequency　magnetic　properties　and　superior　microwave　absorption　performance　compared　to　compounds　with　uniaxial　magnetocrystalline　anisotropy,　due　to　their　higher　Snoek　limit　resulting　from　high　saturation　magnetization　(Ms)　and　large　anisotropy　factor.　In　this　work,　we　investigated　the　structure,　magnetic,　and　microwave　absorbing　properties　of　Y2Fe17-xSix　(0　＜=　x　＜=　2)　with　planer　anisotropy　and　their　paraffin　composites.　Neutron　powder　diffraction　(NPD)　indicates　that　Y2Fe17-xSix　compounds　all　possess　a　disordered　Th2Ni17-type　hexagonal　structure　as　the　primary　phase,　and　the　preferential　order　for　Si　substituting　Fe　crystallographic　sites　is:　12k,　6g,　12j(1),　12j(2),　4f,　and　4e.　At　room　temperature　(RT),　the　57Fe　M　&　ouml;ssbauer　spectra　reveal　that　the　average　hyperfine　field　increases　with　increasing　Si　content,　which　is　proportional　to　the　average　atomic　magnetic　moment　of　Fe.　Magnetic　measurements　show　that　Si　substitution　significantly　raises　the　Curie　temperature　(T-c)　of　Y2Fe17-xSix　compounds,　while　also　increasing　the　M-s　at　RT.　By　studying　the　high-frequency　electromagnetic　properties　of　Y2Fe17-xSix/paraffin　composites,　it　was　found　that　the　real　part　of　permittivity　(epsilon　epsilon　＇)　at　1　GHz　decreases　with　increasing　Si　content,　reducing　by　approximately　40%　for　x=2　compared　to　x=0.　Meanwhile,　the　real　part　of　permeability　(mu　＇)　at　1　GHz　initially　increases　and　then　decreases　with　increasing　Si　content,　reaching　a　maximum　at　x=1.5.　Therefore,　Si　substitution　is　advantageous　to　enhance　the　impedance　matching　of　the　composites,　leading　to　better　microwave　absorption　performance.　Among　all　the　compositions,　the　Y2Fe15Si2/paraffin　composite　exhibits　a　minimum　reflection　loss　(RL)　of　-53.3　dB　with　a　thickness　of　3.0　mm,　and　a　maximum　effective　absorption　bandwidth　(EAB,　RL＜-10　dB)　of　3.95　GHz　with　a　thickness　of　1.06　mm,　making　it　a　promising　candidate　for　high-performance　microwave　absorbing　materials　(MAMs).