To　investigate　the　effect　of　Ca　poisoning　on　Cu-SAPO-18,　a　series　of　samples　with　different　Ca　amounts　were　prepared　by　the　impregnation　method,　and　their　NH3-SCR　activities　were　evaluated.　When　the　Ca　amount　was　0.8　mmol/g(cat),　NO　conversion　at　350　degrees　C　was　40.6%　(lower　than　that　over　the　fresh　Cu-SAPO-18　sample),　which　shows　that　the　catalytic　deNO(x)　performance　was　significantly　decreased　after　Ca　poisoning.　Ca　poisoning　did　not　have　a　great　influence　on　the　structure　of　Cu-SAPO-18,　but　the　formed　CaO　blocked　part　of　the　micropores,　which　reduced　surface　area　and　micropore　volume,　and　further　reduced　accessibility　of　the　active　sites　and　surface　acidity　of　the　sample.　The　total　amount　of　the　isolated　Cu2+　species　decreased　from　62.83　mu　mol/g(Cu-SAPO-18)　to　23.45　mu　mol/g(0.8Ca-Cu-SAPO-18),　which　resulted　in　conversion　of　the　isolated　Cu2+　species　to　Cu2O　in　the　sample　after　the　addition　of　Ca.　In　addition,　the　substitution　of　Ca2+　with　H　or　Cu2+　in　Si-O(H)-Al　or　Si-O(Cu2+)-Al　to　form　the　Si-O(Ca2+)-Al　species　decreased　amounts　of　the　Lewis　and　Bronsted　acid　sites,　which　might　be　the　important　reasons　for　the　drop　in　catalytic　activity.　Both　the　Eley-Rideal　(E-R)　and　Langmuir-Hinshelwood　(L-H)　reaction　mechanisms　existed　over　the　samples　in　the　NH3-SCR　reaction,　but　the　L-H　reaction　mechanism　was　dominant.　The　catalytic　mechanism　over　the　sample　did　not　change,　but　the　reaction　was　slower　after　Ca　poisoning.