The worldwide rivalry of commerce leads organizations to focus on selecting the best project portfolio among available projects through utilizing their scarce resources in the most effective manner. To accomplish this, organizations should consider the intrinsic uncertainty in projects on the basis of an appropriate evaluation technique with regard to the flexibility in investment decision-making along an optimization framework. In the current research here, the problem of project selection under uncertain environment is formulated by using robust optimization model for dealing with the complexities and uncertainties regarding the construction of a project portfolio. First of all, a general mathematical formulation which can address compound real option evaluation is employed to correct the deficiency of traditional approaches to evaluate the worth of multi-step problems. Then, a project selection model is developed by robust optimization, which is effective for solving problems under uncertainty. Finally, by supposing the budget of the organization to be rare, the model maximizes the combinatorial robust optimization worth of projects and is solved according to the combinatorial robust optimization algorithm. A comprehensive example is provided to illustrate the proposed decision approach.