Abstract: By using the sea-floor visualization technique, we can directly observe sea-bottom landforms, surface sediment types and biotic communities in real time. Four kinds of sea-floor visualization technique, namely, sea-floor video, TV-grab, deep tow system and ROV, are introduced in this paper. Great efforts have been devoted to the applications of these techniques in gas hydrate exploration on the northern slope of the South China Sea. Authigenic carbonate rocks that formed by gas hydrate venting and chemoauthotrophic biotic communities such as bacterial mats, bivalves and tube worms that live around gas hydrate vents or percolating outlets have been found on the northern slope of the South China Sea. The distribution area of authigenic carbonate rocks thus formed on this slope is up to 430 km2