Abstract: In the filling process of high stage stope, the strength of in-situ coring samples was much higher than that of the laboratory test blocks.The coring samples of 6 high stage filling stope in Lilou iron mine were selected in this paper and it was found that the in-situ coring strength was 1.59 MPa higher than that of the laboratory-cured specimens.The composition of hydration products in cemented backfill was determined by SEM and energy spectrum analysis, and the consolidation process of the unclassified tailing slurry was further analyzed.Based on the macro-micro test of the backfill, a coupling analysis of the strength difference between in-situ coring samples and laboratory-cured specimens was performed, and the mechanism of self weight pressure on the macro-mechanical properties and micro-pore structure of the backfill was revealed.The research results can provide a theoretical basis for further reducing the cement-sand ratio in the high stage stope.