A method based on SEA for effectiveness analysis of AWACS for low altitude early- warning is proposed. The fundamental principle of SEA is first introduced, and the problem of effectiveness analysis of AWACS, while performing the mission of low altitude early-warning, is described, with the proposition of effectiveness model of AWACS for low altitude early-warning and the emphasis on investigating the calculation methods of effective early-warning for low altitude which describe how to get the measure of performance from system mapping and mission mapping. The validity of the method is illustrated by an example. This will be beneficial to the following research on integrated system effectiveness analysis of AWAC.