Abstract: Stability of overlying strata at goaf under condition of open-underground combined mining had been a key issue in mining engineering technology. Practice situation of a mine in Ordos were analyzed and calculated by using KB LuPeinie theory estimation method, structural mechanics theory calculation method, Platts arch theory estimation method and numerical simulation method, numerical simulation was done on different goaf span and top plate thickness, though combine of several calculating methods and practice production situation, reasonable minimum safe thickness value of overlying strata at different goaf span was obtained, provided reference for reasonable goaf overlying strata thickness design of mine, had important guiding significance for safe production of open-underground combined mining.

Key words: Open-underground combined mining, Reasonable top plate thickness, Goaf span, Maximum tensile stress