Lake Sifangshan (49°22'32.97"N,123°27'49.90"E; altitude in 933m a.s.l.),a circle nearly dried up volcanic lake, located on the central-northern part of the Great Xing'an Range, northeast of China, current northern margin of the East Asian summer monsoon. It is a particularly sensitive region to climate changes and was formed by volcanic eruptions during the Late-Pleistocene ( 0.1280.01Ma). A suite of cores were retrieved from Lake Sifangshan using piston corer in 2012. The cores were correlated using distinctive layers. Then a 482.5cm long sediment core recovered. The cores were split in half longitudinally, and one half of the core was used for geochemical analyses sampled at lcm interval (e.g. stable carbon isotope of bulk organic matter (delta~(13)C_(org.)), total organic carbon contents (TOC) and total nitrogen (TN) contents) to understand the process of changes in the climate condition during the last 15.4ka B.P. The results show a large variation in TOC and TN contents, they were positively correlated (R = 0.99). TOC values may reflect the gradual accumulation of the organic matter in the lake sediment which change from the 1.60% during the last glacial period to 34.40% in Modern Time. The atomic rations of TOC to TN ranging from 10.4 to 18.8 with the average of 14.2, indicating the different contribution from algae and terrestrial plant during different climate stage. C_3 plants account for absolute advantage in the forest around the Lake Sifangshan. The delta~(13)C_(org.) values which is interpreted to reflect effective precipitation variations from -31.79to -22.51The process of the climate changes since 15.4ka B.P. can be divided into six stages according to the stable carbon isotope record of bulk organic matter, TOC content and TOC/TN . During 15.4~14.5ka B.P., TOC content is low ( 1.60% ~4.76%),TOC/TN values changes from 10.4 ~13.8 which may reflect that the original organic matter of the lake sediment was from algal in the lake and terrestrial C_3 plants and the proportion of aquatic plants were higher than terrestrial plants, the delta~(13)C_(org.) have less negative values ( -28.01~ -24.99), effective precipitation is low, indicating a cold and dry period. In contrast, during 14.5~ 12.7ka B.P. which is correspond to Bolling-Allerod period ( B-A),TOC contents and TOC/TN rose significantly and reached their maximum values of this stage around 13.6 ka B.P., the delta~(13)C_(org) values became much more negative ( -31.79~-26.67) and appeared most negative values of the profile around 14. 4ka B.P. ( -31.79),the original organic matter of the lake sediment changed from terrestrial plant to algae and terrestrial plant around 13.6ka B.P.,suggesting that climate has significantly humid-dry variations.