Abstract: As an important coastal economic zone in China, Liaodong Bay carries a large number of nutrients discharged from coastal areas for many years, and the coastal area is seriously eutrophicated. Based on the monitoring data of seawater environmental quality in Liaodong Bay from 2014 to 2017, the reference values of dissolved inorganic nitrogen, active phosphate and their response index dissolved oxygen (DO) in the inshore waters of Liaodong Bay were derived by frequency analysis. Also, the frequency distribution curve was drawn using the special survey data of Bohai Sea of State Oceanic Administration when Liaodong Bay was not been polluted in 1974, and the median value was used as the reference state for verification. Finally, the results of the two methods were compared, and the recommended baseline values of dissolved inorganic nitrogen, active phosphate and DO were comprehensively analyzed and deduced. The results showed that the baseline values of dissolved inorganic nitrogen, active phosphate and DO obtained by frequency analysis was 0.050, 0.002 and 9.61 mg/L, respectively, and the reference states of dissolved inorganic nitrogen and DO in Liaodong Bay was 0.053 and 6.29 mg/L by reference state method, respectively. Compared with the results of frequency analysis and reference state method, the reference values of dissolved inorganic nitrogen obtained by the two methods were basically the same, but DO baseline values were quite different. Considering that the class Ⅰ water quality standard limit of DO concentration in Seawater Quality Standard (GB 3097-1997) was 6.0 mg/L, the recommended baseline values of dissolved inorganic nitrogen, active phosphate and DO in Liaodong Bay was finally determined as 0.05, 0.002 and 6.29 mg/L, respectively.