The Mudui stratigraphic section represents the typical records of sedimentation processes of sand dunes and interdune depressions on the east coast of Hainan Island.Based on high-density sampling and optically stimulated luminescence (OSL) dating of the strata of the section,the grain-size composition,grain-size parameters,cumulative distribution probability curve,and grain-size-sensitivity indexes (SC/D) were analyzed.The analyzed results show that the grain-size features of aeolian sand,weakly developed sandy paleosol,two-facies (aeolian and aqueous) deposits,and lagoon deposits are all different.This indicates four evolutionary phases of the sedimentary environment of the east coast of Hainan Island since 38 ka B.P.PhaseⅠ:38-22 ka B.P.;phaseⅡ:22-17 ka B.P.;phase Ⅲ:17-10 ka B.P.;phase IV:10 ka B.P.Present.The climate experienced the hot-wet/hot-dry,hot-wet/hot-dry,and warm-wet/hot-wet fluctuations,and the sedimentary environment also underwent lagoon deposition,dune and interdune depression deposition,dune stabilization and soil development,shifting sand deposition,and evolutionary processes.