The existing two-dimensional flow field visualizations are all based on structured grid flow field data. This paper proposed a strategy of ocean flow field visualization based on unstructured triangular grid, in which the flow field is expressed by streamline. The main challenge faced by streamline visualization lies in the placement of seed point, namely the initial point of streamline. To meet this challenge, a feature-guided seed point placement strategy was designed based on unstructured triangular grid. Thus, streamline initial points can be placed reasonably to facilitate the expression of flow field characteristics. A hierarchical clustering algorithm based on grid density was also designed. The grid density attribute was introduced to cluster the streamline, which was placed based on the centroid of the cluster. The visualization effect of streamline was enhanced on the premise of preserving the multi-density of FVCOM schema data. The experimental results show that the above methods can effectively retain the characteristics of the flow field, and achieve a good visualization effect for such areas as bay and riverway using the boundary fitting of FVCOM model. On this basis, taking advantage of Cesium engine, a dynamic flow field visualization application was developed based on streamline clustering data. This marks the first attempt to apply FVCOM mode data to dynamic particle flow field, and can produce a good visualization effect.