A 2-deimensional environment management model is established by comprehensively analyzing thecumulative environment impacts of the cascade hydropower development project group from a series of factorssuch as water body,resources,biology,society and economy.Based on the current construction projectmanagement procedures in China,the first dimension（environment management evaluation system）includes the project proposal or pre-feasibility study phase,feasibility study phase,design phase,construction phase, trial production and completion acceptance phase,and cooperation management.At the same time,the second dimension（5levels environment management maturity development model）is established,which includes“disorder level”,“simple level”,“standard level”,“improvement level”,and“lean level”from low tohigh,with the characteristics of each level being redefined.Group decision method is utilized to evaluate theenvironment management maturity of the cascade hydropower development project group and the four-quadrant analysis is made to improve the environment management maturity.Results from the analyses indicatethat for the purpose to improve the environment management maturity,the key improvement should be madein the second quadrant,while the first quadrant level should be maintained at the same time.A case study ismade to verify the model.