Abstract: Shidao Island, the highest one among the Xisha Archipelago, is some 15 metersabove sea level.The sequence of the biocalcarenites occurred on the island is cha-racterized by the alternation of that with cross-beddings and parallel beddings.O wing to the misinterpretation of the sedimentary structures, it has caused so m econ troversaries. T he materials of the biocalcarenites are obviously from the destruction of thecontemporaneous reef complex. Most of the grain components range in medium tofine sands with perfect roundness. T hree kinds of boundary surfaces have been found in the sequence.First-orderboundaries are marked with the occurence of paleosols which is nearly horizontal.T he paleosols, w hick indicate a non deposition period and a change of clim ate, arecharacterized by the dece mentation and phosphorization of the rocks, and the occu-rence of continental snail fossils.Wide distributed rhitholiths demonstrate thegrowth of plant during the stage of pedogenesis. The second-order boundaries are those between dune deposits and interdunedeposits.They are formed by the climbing of the dunes and interdunes under theaction of NE-trade wind.The boundaries sli,;htly dip at an angle less than 10.aga-inst the wind direction and comparable with the boundaries found in modern eoliandeposits. T'he third-order boundaries are the boundaries of costs，which inclinc exclusi-vely windward. Based on the principles of comparative se;dimenlology，she first一order and third-order boundaries are isochronous, but the second一order boundories only of facies. At least two first-order boundaries occur in the sequence of biocalcarenites onthe island.The lower one might be traced on the whole island and is 20-30cm inthickness. The upper one is coincident with the modern topographical surface. The dune deposits, usually 3-7m in thickness, have well一preserved cross-beddin-gs on great scale, including trough cross一beddings, convex cross-beddings and planarcross-beddings. The dip argle of the cross-beddings may reach 35 or so. The interdunedeposits show roughly paralled bedding,but in fact, they are all cross-beddings withvery small dip angle. In conclusion, the coexistence of the three boundary surfaces and the dune andinterdune deposits marks the feature of the eolian biocalcarenits. A facies modelshowingin figure 15 is proposed, which may be used elsewhere, Basedon the data of C¹⁴ dating collected from the previous works, the authorsbelieve that the biocalcarenites on Shidao Island were formed some 3200 years agowhen the sea level stood at a low level，then the island passed a transgression per-iod with alternation of dry and wet weather. All the controversaries might besolved by the model mentioned in the paper.