Abstract: Based on engineering practice of abscission layer mining with flling in Huaibei Mining Area, in order to find out the spatial relationship of flling body of fl y ash in abscission layer, horizontal and vertical migration pathways and solute diffusion characteristics under the condition of coal mining by using the methods of trac er test and numerical analysis, the author studied the storage space, transmitting pathway and solute diffusion characteristics. Results showed that with the advancing of workface, the mining fracture was evoluted dynamically, fly ash slurry was mainly concentrated in the abscission zone, a small amount of slurry was poured into mini ng space by mining fissures and structural fissures. The influence scope of the slurry on the ground water decreased gradually with the change of time, and the effect d egree decreased gradually. Results also showed that, 63 ~ 77 m region of upper roof appeared horizontal abscission zone with large area, which was the main storage space of fly ash flling body. Affected by dilution and purification of groundwater, with 20 years' grouting, the influence of slurry on the quantity of groundwater could be eliminated.