We　propose　and　demonstrate　a　photonic　microwave　signal　harmonic　down-converter　with　image　rejection　capability　via　stimulated　Brillouin　scattering　(SBS).　A　dual-polarization　dual-parallel　Mach-Zehnder　modulator　(DP-DPMZM)　is　driven　by　a　radio　frequency/image　(RF/IM)　signal　and　a　local　oscillation　(LO)　signal　to　realize　equivalent　phase　modulation　and　4th-order　double　sideband　modulation　respectively.　The　optical　carriers　from　the　two　arms　of　the　DP-DPMZM　can　cancel　out　each　other　after　polarization　combining,　thereby　increasing　the　useful　optical　signal　power　in　photodetection.　Since　the　beating　notes　between　the　IM-modulated　signals　and　LO-modulated　4th-order　sidebands　interfere　destructively,　the　down-converted　IM　signals　disappear　naturally,　which　makes　the　down-converted　image　parts　be　suppressed　in　optical　domain.　By　using　an　SBS-based　dual-band　microwave　photonic　filter　to　suppress　the　RF　modulated　-1st-order　sideband　and　amplify　the　+1st-order　sideband,　destructive　interference　can　be　broken.　Therefore,　the　RF　signal　over　frequency　range　of　21-28　GHz　can　be　down-converted　to　intermediate　frequency　(IF)　band,　and　the　image　rejection　ratio　(IRR)　can　be　also　improved　to　more　than　55　dB.　Under　-160　dBm/Hz　noise　floor,　the　SFDR　is　105.1　dB　center　dot　Hz(2/3).