A new sliding mode controller design method is proposed for a class of system with mis- matched uncertainties such that the dynamic function restricted on the sliding surface is completely insensitive to the uncertainties.A sufficient and necessary condition which the system possessing this sliding mode controller should satisfy is explicitly presented.The issue of chattering free is also explored.It is concluded that this class of mismatched term does not bring any chattering problem. Finally,a numerical example illustrates the developed method. A new sliding mode controller design method is proposed for a class of system with mis-matched uncertainties such that the dynamic function restricted on the sliding surface is completely insensitive to the uncertainties. A sufficient and necessary condition which the system possessing this sliding mode controller should satisfy is explicitly presented. The issue of chattering free is also explored. It is that this class of mismatched term does not bring any chattering problem. Finally, a numerical example illustrates the developed method.