Including past, present and future impacts in environmental impact assessment (EIA) of the proposed action, it is the important property of cumulative impact assessment (CIA) that different from traditional EIA. It is also the main trend of EIA improvement. From the area of regulation demands, documentation practice, spatial and temporal boundary, key contents and mitigation measures, this paper analyses the status of CIA both of China Mainland and Hongkong in the practice of EIA. The author suggested that technical guidelines for cumulative effects assessment should be set up in China Mainland and Hongkong, CIA should be included in project, region and strategy environment assessment and cumulative impacts should be list clearly in EIA study executive summary and reported in a separate part of the environmental consequences section. Spatial and temporal boundaries and any cumulative impacts addressed within the CIA process should be provided evidence or analysis to support the conclusion. In order to prevent cumulative effects effectively, the focus on CIA should be put on biodiversity, social and economic impacts and global environmental effects.