Estimating the time of projects in the engineering project management involves some sort of imprecision. Traditional network planning methods cannot solve problems of uncertainty. Based on fuzzy set theory, an analysis of the uncertainty is made in this paper. Triangular fuzzy number is introduced to the project duration analysis, and subjectd degree function of dutation is given. An optimal construction time-cost trade-off method integrating fuzzy theory and genetic algorithms (GAs) is proposed in this paper. A fuzzy model for optimizing the fuzzy network on time-cost is established. Experimental results indicate that the method of fuzzy network planning of time-cost optimization of a certain degree of flexibility and adaptability.