Abstract: The narrow sense and applicable limit of practical salinity scale 1978 (PSS78) and volumetric titration using silver nitrate to measure the salinity of non-conservative ocean water are discussed,It is found that the salinity obtained by electrical conductivity method and chlorinity salinity method are obviously deviated from the absolute salinity (S_a),the density salinity scale (DSS98) proposed by the writers can be extensively used in conservative and non-conservative water samples.The characteristics of the density salinity scale are: (1) The density salinity scale is only related to seawater mass and its buoyant effect and is not influenced by the variation of seawater composition,and so,has high reliability,and repeatability of determination.(2) The salinity values measured on the DSS98 have conservative property.For ocean water samples the salinity values are the same as those determined by the PSS78,for non-conserv ative water samples,for example,samples from industrial sources,the salinity values are closer to the absolute salinity values in comparison with those measured by the PSS78 and the Knudsen method.(3) For a solution withx given solute mass,the solution concentration can be converted into the corresponding salinity by the density salinity scale using the expansion coefficient of the solution and the calibration coefficient of the partial molar volume of the solute.