Based on the basic theories of sediment, flow movement and the diffuseness of temperature and concentration, a 2 -  D mathematic model describing sediment -  carrying flow, temperature and concentration fields used in reservoir, river channels and estuaries was established. The limit volume method and the finite element method were adopted to solve the control equations of 2 -  D mathematic model. The calculation process of this model is stable and computational velocity quick.This model has been widely used in engineerings and detected by field observed results.