This paper analyzes the features of the biological community, succession of dominant species, diversity, and stability of the Yalu River Estuary offshore waters using an ABC curve method combined with particle-size spectrum theory, and establishes a model to evaluate the stability of the Yalu River Estuary ecosystem area. The aim is to understand the ecological health and status of the Yalu River Estuary wetland reserve nature reserve and to analyze problems related to this ecosystem. The results show the structure of the Estuary's biological community is relatively simple; the patterns of succession are obvious for the dominant species and this ecosystem is susceptible to outside interference. Sufficient sunlight, appropriate temperatures and the accumulation of nutrients provide favorable conditions for phytoplankton growth in spring, so microorganisms based on R-countermeasures multiply rapidly (Skeletonema costatum, Asterionella kariana), causing the community to deviate from the point of equilibrium. Rivers constantly supply nutrients from land-based sources in the summer, so the dominant species are replaced by Nitzschia delicatissima. In fall, more nutrients are consumed than are replaced by the river, so the micro bio-based R-countermeasures will be gradually replaced by k-countermeasures (Coscinodiscus spp., Fragilaria spp., Ceratium fusus), the community completes its cycle of natural feedback-driven regulation and returns to equilibrium. Similarly, the supply of high energy phytoplankton leads to zooplankton blooms; small herbivorous copepod (section) larvae have been present in high numbers throughout the year. Based on the ABC curve results and standard biomass spectrum analysis, external disturbances impact the benthic community in summer because migratory waders feed on benthos. At the peak of migration waders have a more significant influence on intertidal food organisms. After migration peaks, the benthic food biomass recovers gradually, and the community gradually tends to stabilize to former population levels. Standard biomass spectrum analysis confirms the nekton community is comprised primarily of small numbers of individuals, and a stability assessment also shows the nekton community is in a serious state of imbalance. The characteristics of the ABC curve show the Yalu River Estuary biological community has three different seasons, but according to W statistics, phytoplankton and zooplankton communities in the spring and summer are affected significantly by external disturbances; this phenomenon is also observed in the intertidal benthic community in the summer, while the nekton community is always in an unstable state. The characteristics of the standard biomass spectrum slope, the residual variance of spectral lines and correlation coefficient of the regression line also confirm these results. The estimation results of the model evaluating community stability in this paper are basically in accord with the above conclusions, indicating the evaluation model is effective and practical. Above all, it indicates the biological community of the Yalu River Estuary has poor stability, and is seriously impacted by external pressures. Inorganic nitrogen and inorganic phosphorus, which come from terrestrial input and marine aquaculture, are the main environmental factors affecting the biological community stability in the offshore wetlands of the Yalu River Estuary.