A method for rendering fluid is provided. First, state information of a plurality of fluid particles is provided, wherein the state information records whether the fluid particles are located above or under a fluid surface and the interactions between the fluid particles and a terrain or the dynamic objects. Then, whether to render the fluid particles in a direction facing a viewer or in a direction parallel to the flow direction is determined according to the information that whether the fluid particles are located above or under the fluid surface. Next, the fluid particles are rendered as a plurality of two-dimensional metaballs according to the interactions between the fluid particles and the terrain or the dynamic objects, and these metaballs are stacked to reconstruct the fluid.