It is hoped that this paper may be a contribution to the solution of further problems arising from the gap between theory and practice. The practical cases in the application of PERT.CPM in Korea was investigated and studied. And the results are presented. These examinations of the actual cases led to a conclusion that in order to apply effectively PERT.CPM and to diminish the gap between the planning and actuality, emphasis must be given to the second factors rather than the first one shown on the network diagram, in the course of the control of the work. These second factors are PERT Status Analysis Report, PERT Emergency and PERT Count Down etc. They are the best methods that can eliminate difficult elements on the critical path, by making the maximum use of slack time.