With the rapid development of offshore oil and gas exploitation and production at marginal oilfields, production facilities of non-pollution oil storage underwater are sorely needed to reduce production costs. The paper gives a general outline of the modes of offshore oil Storage and the status of oil Storage technology underwater. Several modes of oil storage underwater on oil/water separation and replacement are discussed. The scheme on the monitoring system of non-pollution oil storage underwater is put forward. The study is of reference value for the development at offshore marginal oilfields.