Abstract: In order to study the relationship between collapsing ground fissures and geological mining conditions, the forming mechanism of collapsing ground fissures caused by mining in shallow-buried coal seam was analyzed through classified statistics, by adopting the theory of the main roof’s “O-X” type breaking principle and the key stratum theory of ground control. The dynamic development law of collapsing ground fissures was also studied. The engineering example conducted confirmed the reliability of the model. The research showed that when the mining-thickness ratio is less than 30，the fracture zone reach the ground, and the ground cracks easily. If there was no key stratum above the main roof, collapsing ground fissures developed with the breaking of the main roof, the shape of which was similar to the “O” type circle of the main roof. If there was a key stratum, the collapsing ground fissures would lag behind the mining schedule due to the breaking angle of rocks, which meant that there was a log angle of collapsing ground fissures，and the larger the distance between the key stratum and the main roof exists, the greater lag angle was.

Key words: collapsing ground fissures, main roof, thin plate principle, key stratum, lag angle