According to the parametric combination operator theory，a water quality evaluation model was established, and its parameters were optimized with the particle swarm optimization algorithm.The model was applied in the water quality assessment of seawater, groundwater and surface water. Case studies have shown the assessment results of the parametric combination operator models based on the particle swarm optimization algorithm agree basically with those of the conventional assessment methods such as the set pair analysis, BP neural network model and fuzzy comprehensive evaluation. The model has the characteristics of easy calculation and good adaptation to the non -linear water quality evaluation problems．