In　this　paper,　the　principle　of　Attenuated　Total　Reflection　(ATR)　is　used　to　test　and　study　the　silicon　nitride　particle　samples,　and　the　influence　of　particle　size,　shape　and　crystal　phase　on　its　infrared　spectral　performance　is　emphatically　analyzed.　It　is　found　that　the　larger　the　particle　size　of　Si3N4　is,　the　more　its　extinction　peak　moves　to　the　long　wave.　The　smaller　the　particle　size　is,　the　lower　the　extreme　value　of　infrared　transmission　in　the　characteristic　spectrum　segment　is.　For　Si3N4　particles　of　the　same　scale,　spherical　like　particles　can　obtain　lower　infrared　transmittance,　while　cylindrical　like　ones　show　a　wider　range　of　infrared　absorption　bands.　Under　the　same　shape　and　similar　scale,　α　Phase　Si3N4　particles　have　better　infrared　absorption　than　β　Phase.　©　2023　SPIE.