Xiaodonghai coral reef situated in the south part of Hainan Island isa fringe reef.δC

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-dating shows that it developed about 8000 years ago.The texture constituents in reef rocks include reef-building organic frame-work which consists mainly corals

reef-philic organic skeleton fragments

boulders of organic framework

and bioskeleton mud and silt.They areregularily distributed in the certain part of reef flat.Diagenesis of reef rocks has its specific features which is dominated bythe process of organism in which adhesion and encrust acted a principlerole.These diagenetic process reflected different sedimentary environmen tsand their changes. In this paper the authors intend to discribe and discuss the adhesion andencrust of coral

coralline alga

e and foraminifera

and the fill of bioske-leton mud and silt

etc.These process usually were occurred together

andthey are controlled by sedimention-diagenesis environments.The similar diagenetic process are quite common in ancient reef or reefrocks.They are good keys to recognize ancient sedimentary facies and envi-ronments.