I. Introduction
Because of the negative pressure isolation ward's nonlinear system with the characteristics of multiple variables, strong coupling and instability, and the indoor's requirement of uniform directional air flow, stationary temperature and humidity control as well as prevent eddy-making, and it's difficult for traditional control theory and design method to satisfy the control requirement. It has theory advantage to apply modem intelligent control technology into negative pressure isolation ward control system design; with this method we can design a high quality control system [1] to meet the negative pressure isolation ward's safety standards.