The controversy over lithofacies paleogeography of Early-Middle Cambrian affected the hydrocarbon evaluation in southwestern Tarim Basin. According to outcrops, wel and seismic data,the study of sedimentary facies and seismic facies was carried out, and the model of lithofacies paleogeography of Early-Middle Cambrian in southwestern Tarim Basin was reconstructed based on the tectonical background. Control ed by sea level change and paleogeographic pat ern, there developed some facies including shelf, open platform, restricted platform, evaporate platform and gentle slope in Lower-Middle Cambrian. In Late Sinian, low uplifts formed in southern Maigaiti Slope, and thus a paleogeographic pat ern of ocean basin-passive continental margin-intercraton depression distributed from south to north. In passive margin(south to the uplifts), gentle slope facies and shelf facies developed. In the south margin of craton depression(Maigaiti Slope), the tidal-flat facies of restricted platform and evaporate platform mainly developed with thin stratum. In the inner part of craton depression(Bachu Uplift), gypsum-salt lake developed due to hot and dry climate, and poor water circulation. Source rock developed in the residual part of passive continental margin. Reservoir-cap assemblage of gypsum-salt rock and underlying carbonate distributed in Bachu Uplift and Maigaiti Slope. Thus there are good prospects for petroleum exploration in Lower-Middle Cambrian, southwestern Tarim Basin.