According to the N-S equation in fluid mechanics, it is analyzed the rheological properties of strip cast-rolling deforment area with flow function method. The research problem can be simplified into 2-D when the wide of cast-rolling strip are greater than thickness. But, it still difficult to find solution for established two-dimensional partial differential equation directly. A mathematics model of velocity field in the cast-rolling area has been built by flow function method. The model not only satisfies the continues equation, the condition of no-compression and velocity boundary, but it also make the most possible to solute partial differential equation. So, in the future continue research, it has created possible conditions for saluting the mathematics model of average unit compression stress distribution in the cast-rolling deforment area.