Topographic　correction　for　remotely　sensed　imagery　is　an　important　preprocessing　step　in　order　to　improve　the　retrieval　accuracy　of　land　surface　spectral　reflectance　in　mountainous　area.　Various　kinds　of　topographic　correction　models　have　been　proposed　in　the　literature.　Each　model　has　its　advantages　and　limitations.　In　consideration　of　the　limitations　of　the　topographic　correction　models　in　the　literature,　an　improved　Shepherd　topographic　correction　model　is　proposed　in　this　paper.　Diffuse　irradiance　is　an　essential　factor　in　the　physically　based　topographic　correction　model.　While　in　the　Shepherd　model　(originally　proposed　by　Shepherd　et　al.　in　2003),　accuracy　of　the　method　to　compute　the　diffuse　irradiance　is　relatively　low;　therefore,　the　accuracy　of　the　land　surface　spectral　reflectance　retrieved　with　the　Shepherd　model　is　impacted.　In　order　to　improve　the　accuracy　of　diffuse　irradiance,　hence　the　accuracy　of　land　surface　spectral　reflectance,　a　different　method　(named　the　Perez　model),　is　used　to　obtain　the　diffuse　irradiance　with　higher　accuracy　in　the　improved　Shepherd　model.　Landsat　5　Thematic　Mapper　(TM)　imagery　acquired　on　July　12th　2006,　over　the　mountainous　areas　in　the　north　of　Beijing　city,　was　employed　to　retrieve　land　surface　spectral　reflectance　with　the　improved　Shepherd　topographic　correction　model　and　6S　(Second　Simulation　of　the　Satellite　Signal　in　the　Solar　Spectrum)　atmospheric　radiative　transfer　model.　Correction　results　were　tested　with　three　different　methods.　Testing　result　shows　that　the　improved　Shepherd　topographic　correction　model　can　achieve　a　good　correction　result　and　is　better　than　Shepherd　and　C　topographic　correction　model.　What　is　more,　this　improved　model　is　physically　based　and　can　be　applied　to　all　kinds　of　optical　satellite　imagery.