In　this　study,　a　high-strength　silicon　nitride　(Si3N4)　antenna　window　was　successfully　developed　via　selective　laser　sintering　(SLS)　with　cold　isostatic　pressing　(CIP)　after　debinding　before　final　sintering.　The　effects　of　CIP　after　debinding　and　sintering　aids　on　the　bulk　density,　total　porosity,　bending　strength　and　microstructure　of　Si3N4　ceramics　were　examined.　The　results　show　that　the　bending　strength　of　SLS　Si3N4　ceramics　can　be　greatly　improved　by　adding　sintering　aids　between　Si3N4　granules　and　by　CIP　after　debinding.　Optimal　performance　of　ceramics　is　obtained　by　CIP　after　debinding　and　the　use　of　inter-granule　sintering　aids.　The　porosity,　bulk　density,　and　bending　strength　are　18.7%,　3.11　g/cm3,　and　685　MPa,　respectively.　Eliminating　the　pores　by　the　CIP　after　debinding　and　by　inter-granule　sintering　aids　promotes　the　growth　of　rod-like　beta-Si3N4,　which　lock　with　each　other　contribute　to　the　strengthening　of　Si3N4　ceramics.