The invention discloses a method for testing formation water salinity. The method comprises the following steps: (1) grinding a rock core sample to be detected by using a grinding machine; (2) putting the grinded sample into a piece of qualitative filter paper, well wrapping the sample, putting into a Soxhlet extractor, and performing oil washing treatment in pure methylbenzene; (3) after oil washing treatment, adding water into the sample, stirring, and sufficiently dissolving salt into a water solution; (4) analyzing the content of Cl<-> in the solution by using an ion chromatography technique, and converting the content into the concentration of the solution; (5) calculating according to equations: A=Cc*L/1000/M, B=A/(35.5/58.5), and M*B=(M/rho)*10<-3>*phi*0.01*C, thereby obtaining the formation water salinity. By adopting the method disclosed by the invention, the testing efficiency and the precision are improved, the cost of salinity testing is lowered, and the problems that a conventional method is large in error, low in precision and high in cost can be solved.