Abstract: Marine ecosystem health assessment is the core of ocean health research currently. As an open quantitative evaluation framework, the Ocean Health Index (OHI) can provide a scientific and effective method for the assessment and prediction of marine ecosystem health. Based on the OHI framework and combined with the actual coastal environmental characteristics of Liaodong Bay, the model, indicators, and reference points were optimized and the OHI from 1996 to 2020 were evaluated. The results showed that the overall score of OHI ranges from 55.38 to 77.12, with an average value of 64.79 in Liaodong Bay, and presents a certain volatility and a slight downward trend along the time. The scores of different indicators in the OHI framework varied significantly. The Clean Waters and Tourism and Recreation scores are relatively higher, with an average of 89.34 and 89.00, and the Food Provision and Coastal Protection scores are relatively lower, with average scores of 32.65 and 39.07, respectively. The results of influence analysis indicated that Artisanal Fishing Opportunities, Carbon Storage, Food Provision, Biodiversity and Coastal Protection are main factors affect the ocean health of the Liaodong Bay, with the contribution of 18.1%, 15.7%, 14.5%, 13.3% and 12.1%, respectively. Forecasts of future trends indicated that Natural Products, Species, Fisheries, Coastal Protection and Carbon Storage would be in a negative direction, especially the decline trend of Natural Products represented by sea salt and sea chemicals.