We talk about some topics on nonlinear fluid-dynamical equations. The main topics include: 1)the singularity formation and global regularity of an axisymmetric model for the 3D incompressible Euler and Navier-Stokes equations; 2)Asymptotic limits of compressible Euler-Maxwell equations for electro-magnetic; 3) Quasineutral limit of Drift-diffusion models for semiconductors. The related problems are surveyed and some recent results will also be reviewed.