Abstract: The type specimen of Sinogathus gracilis is restudied. Some characters which former workers were not noted are replenished. Among the new discoveries the external auditory meatus interlinked with the cavity of middle ear by an opening at the bottom of extemal auditory meatus, and the side wall of braincase encircled completely by the laminae of bone are to paleontologists and evolutionary biologists. The result of CT scanning the type specimen of S. gracilis is satisfactory for us as follows: l) An exotic in the stuff in cavity of olfaction is found. 2) A trigonal region in the upper part on the corona section of the braincase, a structure unknown before, is tried to explained as the frontoparietal sinusis.