Abstract: In order to study strata movement and stability where coal-pillar under water, building or railway is replaced by gangue backfills of different compactness, spring principle and elastic-plastic theory are used to analyze the compression mechanism of gangue backfills assupporting bodies, and related formula for the early stage compressionis obtained. The compression value and the equivalent miningheight for different compactness is obtained based on compaction principle ofgangue backfills and rock mechanics. In a engineering example, thetheoretical calculation and the numericalsimulation are used to analyze strata movement for gangue backfills of different compactness. It is shown that the roof subsidence andthe equivalent mining height of quadratic strata movement steadilyincrease with the decrease of compactness degree of gangue backfills.When the void ratio is about 0.55, the increment speed of equivalent miningheight becomes very sensitive and the rising tendency of the maximum sidedisplacement become marked.