In this paper, a comprehensive fuzzy multi-objective model is presented for generation expansion planning problem considering uncertainty in objective functions and demand constraint. The purpose of the model is determining the optimal generation amount in existing and new generation units along with calculating the transmission energy volume and required amount of imported fuel regarding emissions and environmental impacts. As the proposed model considers four fuzzy minimization objective functions, a fuzzy linear programming approach is applied to solve the proposed model by transforming the fuzzy multi-objective model to a crisp single objective optimization problem. A case study is presented to illustrate the impacts of different factors such as changes in prices and environmental risks, etc.