Abstract: A generation capacity planning model for power systems with renewable energy resources is proposed to consider the base-load cycling capacity constraints. In this model,the daily base-load cycling capacity constraint in the planning year can be satisfied through dispatching the optimal generation capacity mix. The combination of screening curves method and Lagrange relaxation method is applied to solve this model. In addition,to investigate the impacts of the CO₂ emission cost on the optimal generation capacity mix and base-load cycling capability,the CO₂ emission cost is introduced in generation cost. Numerical simulations are presented to verify the reasonableness and effectiveness of the theoretical analysis. The simulation results demonstrated that it is quite necessary to consider the base-load cycling capacity constraints and environmental costs in generation capacity expansion planning for power systems with high penetration of renewable energy.