A model for plant operating procedure based on flowchart and success logic tree has been developed. The tasks in procedures are classified into orthogonal actions and checks, which play the role of building units of the flowchart as well as an execution unit of procedures. Arrows relate actions and checks to indicate proper workflow. An action or a check is further decomposed into basic instructions considering function allocation between man and computer, characteristics of tasks, etc. N-out-of-M operator combines the instructions within a success logic tree. The flowchart and the tree are comprehensible, transparent, and dynamic. Computers support operators to execute the instructions. The effort to make the tree in allowable states is the driving force for an action or check to be executed successfully. This model improves understandings of procedures, minimizes context switching, and maximizes the usage of computers. Finally a computer based procedure complying with the model was implemented and evaluated with procedures after reactor trip. (C) 2003 Elsevier Ltd. All rights reserved.