Oyster　shell　powder　was　used　as　the　admixture　of　ordinary　portland　cement.　The　effects　of　different　addition　amounts　and　grinding　ways　on　the　strength　and　stability　of　cement　mortar　were　discussed　and　proper　addition　amount　of　oyster　shell　powder　was　determined.　The　structure　and　property　changes　of　cementing　samples　with　different　oyster　shell　powder　contents　were　tested　by　XRD　and　SEM　means.　The　results　revealed　that　compressive　and　rupture　strengths　of　the　sample　with　10%　oyster　shell　powder　was　close　to　those　of　the　original　one　without　addition.　Stability　experiment　showed　that　the　sample　prepared　by　pat　method　had　smooth　surface　without　crack　and　significant　expansion　or　shrinkage　after　pre-curing　and　boiling,　which　indicated　that　cementing　material　dosed　with　oyster　shell　powder　had　fine　stability.　XRD　and　SEM　observation　showed　that　oyster　shell　independently　exists　in　the　cementing　material.