Objectives The salinity characteristics of sewage under different treatment processes in large-scale dairy farms were studied to provide theoretical basis for the utilization of manure resources. Methods The sewage treated by typical processes including milking parlors, urine and solid-liquid separation from 17 dairy farms in Hebei Province were collected. The content of Cl^-, SO₄^2-, Na⁺, K⁺, Ca²⁺, total salinity and electrical conductivity were determined. The correlation between electrical conductivity and salt ions was analyzed. Results The components of inorganic salt in the urine of dairy farms were mainly Cl^-, SO₄^2-, Na⁺ and K⁺. With the advancement of treatment technology, the content of inorganic salt gradually decreased after solid-liquid separation. The content of salt in the sewage from the milking parlors was generally low, with only a slightly higher content of Cl^- (436 mg/L). There were significant differences in the content of total salinity and electrical conductivity among different stages of sewage, and the content of total salinity and electrical conductivity in urine was significantly higher than that in the milking parlors and solid-liquid separation, with values of 52.2 g/L and 23.3 mS/cm, respectively. The results of correlation analysis showed that the content of total salinity was significantly positively correlated with electrical conductivity, Cl^-, SO₄^2-, Na⁺ and K⁺, while the ion with the weakest correlation was Ca²⁺. Conclusions The content of inorganic salt ions and total salinity in urine from large-scale dairy farms was the highest, followed by solid-liquid separation, and the lowest in milking parlors. The electrical conductivity, Cl^-, SO₄^2-, Na⁺ and K⁺ can characterize the characteristic factors for studying the salinity in sewage from large scale dairy farms.