The Dabusu Lake, located in the Songnen (Songhuajiang River-Nenjiang River) Plain, northeastern China, is a closed tectonic fault lake.The investigation on the geomo rphology and depositional ty pes of the basin revealed that the evolution process of the Dabusu Lake was signif icant for interpreting regional envi ronmental evolution. On the basis of the investigat ion as well as ¹⁴C dating, we concluded that the Dabusu Lake was formed in late-Pleistocene.In early times of lake evolution, the Dabusu Lake was a deep lake.Since Holocene, the lake level fluctuated with two enlarging periods and two shrinking preiods, showing that the lake has undertaken two complete deposit ional cycles of lake advance and ret reat.Since mid-Holocene, due to the dryer climate and stronger wind force, the lake level dropped and lake shrank.From then on, the lake gradually turned into a salty lake, which was rare in Northeastern China.