The paper presents an approach to design an intelligent information support system to be used as a human-operator assistant to control large complex industrial plants. Tasks and structure of such an intelligent information support system (IISS), IISS design stages, methodology of IISS design, toolkits for IISS design are considered. A flexible simulation complex (FSC) as such an intelligent toolkit has been presented. The complex is used as a “kernel” of IISS for human-operators of a nuclear power plant. A new approach to abnormal situations with regard for the heuristic regularities of human-operator thinking process is proposed. The regularities are revealed on basis of recording the motions of the human- operator eyes over the information field of the control board and processing the experimental data obtained. For data processing, a probability theoretical approach is used based on involving the notion of consistency of measures of dependence of random variables.