The robust control law for gas tungsten arc welding dynamic process,which is a typical sampled-data system and full of uncertainties,is presented.By using the Lyapunov second method, the robust control and robust optimal control for a class of sampled-data systems whose underlying continuous-time systems are subjected to structured uncertainties are discussed in time-domain.As a result,some sufficient conditions of robust stability and the corresponding robust control laws are derived.All these results are designed by solving a class of linear matrix inequalities(LMIs)and a class of dynamic optimization problem with LMIs constraints respectively.An example adapted under some experimental conditions in the dynamic process of gas tungsten arc welding system in which the controlled variable is the backside width of weld pool and controlling variable pulse duty ratio,is worked out to illustrate the proposed results,it is shown that the sampling period is the crucial design parameter.