The invention discloses a device and method for removing water soluble salt in crude oil. The device comprises a crude oil pipeline and a crude oil filter, at least one separation system and a sand filtration tower which are sequentially arranged on the crude oil pipeline; each separation system comprises a demulsifying agent pipeline, a liquid membrane washing contactor, a membrane-tank connector and a desalting separation tank, wherein a washing circulation pump is arranged between the desalting separation tank and the liquid membrane washing contactor to form a washing water circulation loop. According to the device and method, the number of the separation systems can be selected according to the types of the crude oil to be treated, it is guaranteed that the crude oil obtained by being treated through the device meets the industrial requirements, the usage amount of washing water and demulsifying agents can be decreased in use, the equipment size of desalting separation pipes is reduced, therefore, the production cost is lowered, the usage floor area of the device is reduced, and the difficulty and cost are lowered when a technology is upgraded and improved.