New product portfolio management (NPPM) is the dynamic decision process of evaluating, selecting, prioritizing, and allocating resources to product development projects. The New Product Development (NPD) project decision process deals with uncertain and changing information, dynamic opportunities, several goals and strategic considerations. Stage Gate process is a template that leads a new product project through the various steps from idea to launching and helps manages for the new product development process to improve effectiveness and efficiency. In this study a risk simulation and optimization model is created to select NPD projects by considering three step stage gate concept. In application, the model is applied for a company in portfolio management processes by considering uncertainty.