Abstract: The properties of equilibrium points are analyzed by the singular point theory,and the non-existence of closed orbit is discussed in view of Dulac function.By using Hopf bifurcation theory,some sufficient conditions for the existence of limit cycles are obtained.Furthermore,with the theorem Л.А.Чеpkac and Л.И.Ж.илeвыч,some sufficient conditions for the uniqueness and stability for limit cycles of such systems are obtained.

Key words: planar system, limit cycle, existence, uniqueness