The invention provides a device and a method for determining fluid salinity in porous mediums. The device comprises a conductivity meter, a sand tank and a water supply device. The sand tank is an organic glass tank, and water-containing mediums are filled into the sand tank. An organic glass separating plate which is drilled with eyes and attached with a microporous metal screen is respectively placed at both ends of the sand tank. The front part of the sand tank is provided with an electrode inserting hole and is provided with an electrode of the conductivity meter. The device is characterized in that the standard water-containing mediums are coated on the outer surface of the electrode of the conductivity meter; the solution salinity of the water-containing mediums can be directly determined in a continuous and quick way. The device has the advantages of simple structure and convenient operation. The change of the flow field is avoided during measurement. The method is simple and convenient, and the testing precision is enhanced.