Because of controlling soil and water loss effectively, vegetation construction is regarded as one of the most effective and fundamental methods. The coverage of community is anindicator of measuring the quality of vegetation community for controlling soil and water loss. Effective coverage, critical coverage and potential coverage are three stages in the course of development of vegetation community. The concept and determining methods of “ three coverage” are expounded in detail. It is thought that the coverage of a vegetation community should reach the effective coverage(lower limit) or critical coverage(upper limit) in the construction of vegetation in the soil and water loss region.