Abstract: The well-developed Devonian strata in the Longmen Mountain area, Sichuan is characterized by continuous sequences, good exposures, huge thickness and abundant well-preserved fossils. However, there is still debate about transgression direction and palaeogeography during the Devonian. The data at hand show that during the Devonian, it is impossible for the sea water of the study area to come from Guangxi and Yunnan in the south or from the Qinling Mountain area in the northwest. Furthermore, there was no remnant sea in this region during the period. On this account, the following two inferences are drawn by the author:(1) The Longmen Mountain area was structurally a terrane during the Devonian, and the Devonian strata exposed in this region at present are not autochthonous deposits; (2) The area lay on the continental margin during the Devonian, instead of to the south of Liujing, Guangxi. It is possible for sea water to get to the Longmen Mountain area at first, and then to Liujing, Guangxi. Only after rotating at an angle of 90 degrees, can the whole land mass be in the present-day position.