Marine oil spill has caused pollution damage to the ecological environment, which constitutes a major threat to the safety of the marine environment and human health. Scientific assessment of oil spill pollution damage can play an important role in providing basis for damage repair and compensation arbitration. In order to achieve this goal, it is urgent to strengthen the research on the causality of oil spill pollution damage and the related theories, technical methods and operational application of the judgment methods and criteria. To this end, based on the statistical analysis of the proportion of each fraction and the classified components and contents of different crude oils, this paper constructs the statistical mean index system of oil spill components. And based on the WHO/IARC risk assessment of human cancer caused by chemical substances, this paper reveals the causal relationship between the different types and degrees of marine ecological environment damage caused by different types of oil spills. A damage mechanism analysis method based on the environmental fate of oil spill and persistent organic pollutants (POPs) toxicity theory is then proposed, and a causal relationship determination method of marine ecological environment damage is established, which includes four kinds of judgment criteria of accident occurrence, component content, classified consequence, temporal and spatial distribution and corresponding index system. The overall framework of marine ecological damage assessment model system is proposed, including causal relationship determination model, multi type auxiliary assessment model, investigation and test diagnostic assessment method and operational process, as well as damage baseline and degree determination criteria and index system. In addition, this paper further designs the construction scheme of multi type auxiliary evaluation model, damage baseline and degree judgment criteria and index system. Aiming at the problems of causality judgment and damage degree quantification of seawater quality index, which is the representative vulnerably damaged factor in the auxiliary evaluation model, an oil spill weathering water quality impact evaluation model based on scale-down simulation test of oil spill weathering is constructed. The area exceeding the water quality standards of different classes caused by the oil spill accident and the change and the situation of peak value of the area exceeding the water quality standards of different classes actually monitored before and after the accident are adopted as important indicators in order to determine the causal relationship of damage and evaluate the degree of damage. Through the investigation of oil spills and hazardous chemicals accidents happened in the Bohai Sea and the Yellow Sea, such as ″Tazman Sea″ and Dalian ″7.16″ oil spills, the application research of judgment method and model was carried out, and the model parameters were calibrated. Both the model and the actually monitored results show that there is a significant correlation between the area increment exceeding the water quality standards of different classes and the actual time of oil spill happened in the Bohai Sea and the Yellow Sea with connectivity. Comprehensive judgment shows that there is a close causal relationship between the oil spill pollution damage and the time and location of the pollution accident happened, the connectivity and diffusion conditions of the sea area, the total amount of oil spilling into the sea and the persistence of environmental pollution.