A cognitive information processing model has been developed.  It consists of a perceptual processor, a cognitive processor, a motor processor and a short-term, a working, and a long-term memory. The model is installed on a PC to analyze the visual process of the operator monitoring the overview panel of plant simulator. Visual process is decided by characteristic of panel information,  operator's factors,  and parameters of perceptual processor and so on. The simulation results coincide qualitatively with observations of actual plant operations and simulator training. This model can be used to analyze the generation mechanism of various types of human errors.