Abstract: Pre-backfill without coal pillar technology in roadway can effectively solve the waste of resources in the roadway cutting along goaf with thin pillar. This article described the principle of mining method without coal pillar. The article also numerically simulates the stress distribution and distortion and failure characters of surrounding rocks during the “second mining” when the new technology is used, and summarizes the mechanism of backfill during the “second mining”. Results show that the filling body has complex stress situation and maintains high stress during the whole process of the “second mining”. Meanwhile, the stress peak of this working face is transferred to the solid coal side. In the roof of gob-side entry, top coal that near the narrow pillars drops because of compression and shear failures. At the same time, shear dislocation layer occurs between the roof layers; the coal sides experience compression and shear failures.