Abstract: Computer control systems with nonlinear elements (NCCS) are very tough to be described and analysed since the sampling and nonlinear elements are involved in the same system.Neither linear sampled theory nor continuous non-linear system analysis technique can be used to describe such a system properly.In this paper the method presented,however,is capable of describing NCCS in S Domain and analysing its oscilation.The range of application and the precision of the method is given.Simulation result for a practical example is cited to show the performance of the method.