The Laichichong (Lai Chi Chong) Formation outcrops in the Northeast Sedimentary Rock Region of the Hong Kong Global Geopark. It is composed of the late Jurassic volcanic rocks, sedimentary rocks (developing typical convolute beddings and slump structure) and volcanic rocks from the bottom up, and is very rare in Hong Kong as well as in the Mesozoic volcanic zone of Southeast China Continent. Stratigraphic profile measuring implies that its diagenetic process include the early Plinian eruption, the middle caldera lacustrine deposition and the late Plinian eruption, in which the caldera lacustrine deposition was predominated and volcanic eruption played an additional role. Sedimentary rocks formed during the middle stage were highly silicified and carbonized due to the late Plinian eruption. Special rock assemblage and geographic environment of the Lai Chi Chong Formation provide important clues for understanding Mesozoic volcanism and deposition in Southeast China Continent.