The Paleozoic is the most favorable horizon for exploring giant hydrocarbon reservoirs in the Tarim Basin, northwestern China. Lithofacies and paleogeography of the Early Paleozoic in the basin was researched based on 48 wells which reached or penetrated the Paleozoic, 9800 km seismic profiles, a large amount of isotopes and trace elements composition analyses and other relevant data. Eight samples of lithofacies and paleogeography of the Cambrian and Ordovician in the basin were filed with the unit of epoch and age in order to discuss the sea-level change characteristics qualitatively. Furthermore, the sea-level fluctuation during the Early Paleozoic in the basin was studied quantitatively with the help of sedimentary geochemistry. The study reveals that there were two long-termed regressions and retrogressions during the Early Paleozoic in the basin with one in the Cambrian and the other in the Ordovician. Each regression and retrogression consists of two high-frequency sea-level fluctuations. The biggest regressions occurred in the early Early Cambrian and the early to middle Late Ordovician respectively, and the biggest retrogression occurred in the late Middle Cambrian, the end of the Late Cambrian, and the early to middle Late Ordovician respectively. From the development of the karsts in stratigraphic frameworks we can draw the same conclusion as above.