A pressure and flowrate control system for a supercritical fluid extraction process was designed and its performance was investigated. First, a dynamic model was set up using performance equations of the control valve and the compressor, and a state equation of the supercritical fluid. From this model, pairs of manipulated and controlled variables which give least steady state nteraction were determined through the relative gain analysis. These pairs, however, showed significant dynamic interaction when they were connected in closed loops. To solve this problem, the control pairs by the relative gain analysis were reassessed rigorously using the inverse Nyquist array method and compensators for noninteracting control system were constructed. Simulation study showed that the resulting compen-sated system had much better closed loop responses than those by the relative gain analysis.