Abstract: This study describes a multivariable H robust control approach, for an ill conditioned, difficult to control system, given by a plasma chemical reactor CF4/O2. The control of such a system resulted, in the past, in a slow, oscillatory coupled response. The goals of applying H robust control, is the achievement of a decent smooth response with minimum oscillations and overshoot. In the pursuit of this goal, we proceed to the quantification of uncertainties affecting the plasma process. Then, the robustness conditions in closed loop, to be achieved, are clearly stated. Only then, the H algorithm is applied, after the construction of the augmented system resulting from the standard process form. The results obtained showed, clearly, the advantages of the H robust control approach, within the robustness a-priori set conditions.