Objective: To observe and explore the clinical efficacy and safety of tolvaptan in treatment of decompensated hepatitis B cirrhosis induced diluted hyponatremia. Methods: Ninety-two cases of decompensated hepatitis B cirrhosis patients from May 2015 to October 2016 were enrolled in the study and were randomized into treatment group (47 cases) and control group (45 cases) according to the random number, patients in control group were treated with conventional therapy and spironolactone plus hydrochlorothiazide treatment, the treatment group received conventional therapy and tolvaptan treatment, 7 days for a treatment course, blood Na+ concentration, 24 h urine volume after treatment for 3, 5, 7 d and variations of liver and renal function before and after treatment of the two groups were compared; besides, adverse reactions were noted. Results: After treatment for 3, 5, 7 d, blood Na+ concentration and 24 h urine volume of treatment group were all significantly higher than the control group, the differences between groups with statistical significance (P<0.05). After 7 d treatment, the liver function of the two groups were significantly improved compared with pretreatment (P<0.05), and no significant variation in renal function. There were no significant differences in liver and renal function between the two groups after 7d treatment (P>0.05). Two groups with incidences of thirst (8.5% vs 6.7%), frequent micturition (2.1% vs 2.2%), dizziness (2.1% vs 4.4%) were similar (P>0.05). The treatment group had 1 case suspend medication for blood Na+ concentration and urine volume increased significantly after 5 d treatment. Conclusion: Based on conventional therapy for decompensated hepatitis B cirrhosis induced dilution hyponatremia patients, tolvaptan added can significantly increase urine volume and blood Na+ concentration, and adverse drug reactions can be controllable.