CLVI has the fastest efficient of densification in the preparation of high temperature composites, compared with traditional isothermal CVI technique. In this paper, the internal temperature field of the preform during the process of CLVI was tested synchronously through multiple thermocouples. The change rules of the temperature filed inside the preform was got by analyzing the data obtained from the above test through Origin software. The liquid hydrocarbon keeps the temperature of the outer preform constant at its own boiling point, whereas the inner part of the preform is hot enough to pyrolyze the vaporized carbon precursor, causing a steep thermal gradient through the preform thickness. The thermal gradient along the radial direction in the preform can get about 1000°C during the deposition. In this case, densification occurs preferentially inside the preform, and then outward.