  Based on the Lorenz model derived from the equations of hydrodynamics of
nebula, we discuss the formation of binary stars by the qualitative analysis
theory of nonlinear equation. Here the two wings in the Lorenz model form just
the binary stars, whose Roche surface is result of evolution under certain
condition. The nonlinear interaction plays a crucial role, and is necessary
condition of the formation of binary stars and of multiple stars. While the
linear equations form only a single star. Moreover, the Lorenz model may be
obtained from synergetics yet, and some dynamical equations of the order
parameter can also form the binary star system.
