Abstract: As a main lodging of surface substances, lake sediments continuously and sensitively record information of regional climate and environment with annual to decadal resolution. The sediment core of HLC with a length of 112 cm was taken from deep water location in Hongze Lake in 2003,the sediment were cut at interval of 2 cm and were measured for grain sizes by the particle-size analyzer "Mastersizer 2000"made in England. Based on accurate dating by ²¹⁰Pb,the authors reconstruct the dry-humid transformation history of the regional climate according to the vertical profile of sediment particle sizes, which provides a new effective way for recovering the century-scale climatic changes, the following conclusions are drawn: (1) By the analyses of the grain-size parameters of the Hongze lake sediments, three stages of environmental changes since 300 years ago have been distinguished. They are:Ca.1720-1795A.D., the amount of rainfall was less and weather was drought; Ca. 1795A.D.-1890A.D., as a whole, the average grain-size was decrease, the weather was drought in this stage but Ca.1886 A. D. the flux of water into Hongze Lake was increased; Ca.1890 to current, the changes of grain-size parameter was acute and frequent and this changing phenomenon perhaps instead of the environment fluctuate in shorter periods. (2) During long time-scale studies, lake level is the most important factor domination sediment grain size. Sediments are finer during the humid period of high water level because coarse particles cannot be transported to the lake's deep-water part. On the contrary, during short time-scale studies within a given climate period, rainfall change becomes the key factor determining sediment grain size because the level is basically constant. When rainfall is heavy, runoff flow is strong enough to bring coarse terrestrial particles to the sampling location, resulting in large grain sizes. (3) Grain-size parameters changes is relate not only with the natural environment changes but also with the human activities such as Huanghe(Yellow) River changing channel and some brakes were built up around the lake.