Abstract: By analyzing the mechanical properties of backfilling slurry and the special features of airtight wall，it is found that the airtight wall not only supports the pressure from the filling slurry，but also filters the water in the structure.What's more，its structure is closely related to the mine filling technology，which impacts the production capacity and cost-benefit.The mechanical properties of backfilling slurry and the failure mechanism of airtight wall have become the key of airtight wall design.Then，the calculation model of airtight walls is induced.Lastly，the limit equilibrium conditions are built by combining Ken Lang theory with single-phase liquid and loose medium as carrier mediums.The changes about properties and physical state of slurry are analyzed to optimize the structure and force calculation of the wall.The study above provides a more economical and reasonable theory for design of airtight wall.

Key words: Filling airtight wall, Loose medium, Calculation model, Limit equilibrium, Stress analysis