Scale, as the measurement of geographical phenomena and historical events in time and space, is the core of the cross-integration of geography and history. The scale thought is also one of the basic geographical ideas that middle school students must master. This article takes "ecological security" as an example, constructs the implementation path of interdisciplinary teaching of geography and history under the scale thought, in order to guide students to understand the human-land relationship in different periods, and thereby establish an ecological security view and cultivate students' geographic key competency.