Based on the survey of floating population of 100 key villages（communities）in Beijing’s the rural-urban fringe zones，this paper describes the present situation and changes of the population structure in the areas where the floating population is concentrated. And analyzes the causes and types of settlement，finds out and explains in detail the “barrier lake” effect and its internal mechanism under the background of dissolving the function of non-capital city，and under the action of continuous remediation to the rural-urban fringe zones. Finally，following the concept of “good governance”，the paper puts forward the rethinking of the governance of the rural-urban fringe zones.