The invention provides an underwater leaked oil flexible collection cover which comprises a flexible collection cover, a buoyance assembly, an outlet pipe, cables, a counterweight device or a counterweight frame. The flexile connection cover is made of thin-film-shaped waterproof materials. The underwater leaked oil flexible collection cover can be folded to be stored at ordinary time, and the counterweight device and the outlet pipe can not be connected with the flexible collection cover temporarily at the moment. The outlet pipe is assembled well before the underwater leaked oil flexible collection cover goes to sea to be used, and at least the counterweight device or the counterweight frame capable of enabling a complete device to sink smoothly is connected in a matching mode. When the underwater leaked oil flexible collection cover is used, the flexible collection cover is unfolded to be covered above an oil leaking point, and the cables are tied on a fixed structural object/or a temporarily arranged anchor and a weight under the sea in a distributed mode. Collected leaked oil is output through a pipeline. The complete underwater leaked oil flexible collection cover is light in weight, foldable, detachable, easy to store, transport and install and particularly suitable for early rapid application at emergency conditions and gains time for adoption of subsequent measures.