In more and more popular physically-based fluid animation field, there are many methods for individually simulating Newtonian fluid or viscoelastic fluid, but few unified techniques are available for both. Based on Smoothed Particle Hydrodynamics, this paper presents a novel unified method for animating both fluids by introducing an additional elastic stress term to the traditional Navier-Stokes equation. The experimental results demonstrate that this new method is not only effective and easy to implement, but also has good controllability. Different viscoelastic and various kinds of fluids behaviors can be obtained easily by adjusting the very few experimental parameters.