Enhancing the operator¡Çs ability to cope with emergent situation is very important in keeping the reliability and safety of Nuclear Power Plant operation. In order to make operators diagnose the fault cause promptly and accurately and execute the emergency operation procedure correctly, the result of diagnosis support system should be not only correct, but also understandable to get operators¡Ç trust for the system. With a clear presentation and an explicit instruction by supporting system, operators can easily know what happened in the plant system and perform the emergency operation procedure correctly and quickly. In this paper, a new concept of alarm analysis and supervisory system by the combination of Multilevel Flow Model (MFM) and Ecological Interface Design (EID) is proposed aiming at enhancing the understandability and trust of operator by showing the presentation of diagnosis result and confirm flow of operators in a more straightforward way than simply showing all diagnosis result by MFM. By this concept, MFM gives the means-end, parts-whole representation of the plant process and perform alarm analysis by causal dependency graph, and the clear relationships among different parameters which are directly related with the diagnosed root cause of the anomaly are shown by the form of ecological interface so that the operator can confirm the diagnosed result by causal dependency graph on MFM intuitively on a comprehensive display presentation.