Optimizing the network diagram under standard of time and costisone of the effective solutions to shortening the execution time of each task list or an entire project with the lowest total cost. This method is meaningful and necessary in order to bring high economic efficiency in the organization, planning and implementation of projects in the market economy, which always has highly competition on price. This paper presents optimization methods according to criteria of time, cost on network diagrams using genetic algorithms combined with penalty cost method to find the optimal and feasible alternative.