This thesis develops a heuristic approach to detect the key technology among new technologies which will be developed to attain a normative objective (developing a special product). In this study, the key technology with respect to the time is defined, and an approach to detect the key technology by simulation and Delph data is presented. The simulation procedure provides the probability of development time for the final product and all technologies which affect it``s development directly or indirectly using Delhi data. And it also provides the range of occurrence time for individual technology in contrast that a expert``s estimate to occurrence time is only one point. Two measures, criticality index and goodness of fit, to compare and analyze differences between earliest and latest occurrence time are used. The data for key technology which is detected by this procedure gives priorities of R\&D planning and aids the R\&D planner or project manager in resource allocation.