Abstract: Due to the intensification of human activities, the eco-hydrological regime in the lower reaches of Mekong River has changed. In order to quantitatively evaluate the hydrological regime alteration of the lower Mekong River, based on the daily flow data (from 1961 to 2020) at Kratie hydrological station, Mann-Kendall mutation test and sliding t test method were used to analyze the trend characteristics of annual mean flow, and the RVA method was used to evaluate the eco-hydrological regime alteration and its ecological impact in the lower reaches of Mekong River. The results showed that: ① The annual mean flow at Kratie station generally decreased first and then increased. The mutation year occurred in 1996, indicating that the impact of human activities on the hydrology of the downstream in Mekong was intensified since 1996. ② The overall hydrological change degree at Kratie Station in the lower Mekong river was 57.99%, which was a moderate change. The hydrological indicators in the dry season were most affected. ③ The intervention of human activities has increased the flow of the lower Mekong River in the dry season, and imposed little impact on the flow in the wet season. It is necessary to enhance the monitoring on water ecology to prevent the adverse impact of hydrological regime alteration on ecology. This study can provide theoretical support for the study of hydrological regime alteration in the lower reaches of Mekong River.