An evaporator for submerged combustion and delayed evaporation, a method of the same and a system of combined evaporation devices, the evaporator for submerged combustion and delayed evaporation comprises: a housing formed with a space for containing an evaporating liquid; a separator plate arranged in an interior of the housing and dividing the housing into a heat transfer (submerged combustion) area and an evaporation area; a vapor chamber located above a liquid surface of the evaporation area; a flue gas chamber located above a liquid surface of the heat transfer area, wherein the flue gas chamber is provided with a flue gas outlet, the flue gas outlet is provided with a pressure valve which is capable of controlling a gas pressure within the flue gas chamber such that a gas pressure within the flue gas chamber is larger than a gas pressure within the vapor chamber.