Tracking regime shifts and procession of transforming ecosystem is an essential and efficient approach for lake management. In this study, a sediment core labeled XJ2018 (31°23'48.8″N, 119°43'33.8″E) was extracted and analyzed for reconstructing the past transitional processes of Lake Xijiu based on the biological (chironomid subfossils) and geological parameters (total nitrogen and total phosphorus). The changes of chironomid subfossil assemblage structure and the results of STARS based on PCA scores of chironomid assemblages both indicated Lake Xijiu had undergone a distinct stable-state transition in the past 40 years. The RSI index combined F-test revealed that an ecological shift took place in 1990s. Before 1990, there are high aquatic vegetable coverage and the chironomid was characterized by the macrophyte-related taxa (Cricotopus trifasciatus and Dicrotendipes spp.), thus the ecosystem in this stage can be regarded as plants dominated clear state. In 1990-2000, a remarkable ecology shift was detected due to the enclosed fish-farming and rapid agriculture developments, the macrophyte-related taxa have been gradually reduced while the euryphagic taxa (Tanypus chinensis and Microchironomus tabarui) has increased and gradually occupied a dominant position. The water status had been changed into the phytoplankton dominated turbid-water. During 2000-2010, the lake ecosystem deteriorated further and the macrophyte-related taxa were almost disappeared. After 2010, The reappearance of some macrophyte-related taxa and the decline of the euryphagic taxa indicate that with the implementation of the ecological restorations and managements, the environment of Lake Xijiu has improved slightly, but the phytoplankton dominated turbid-water was still sustained.