Generation planning has been extensively investigated and applied to practical power industry. This paper presents the generation planningmodel of Jiaotong Automatic System Planning Package (JASP) of Xi’an Jiaotong University, China. JASP decomposes the generationplanning problem into a high-level power plant investment decision problem and a low-level operation planning problem and solves them bya decomposition-coordination method. Lagrangian Relaxation is used to solve the power plant investment decision problem and probabilisticproduction simulation is used to solve the operation planning problem. The generation planning model of JASP can be easily extended to thecontext of market liberalization. Simulation results show that JASP can not only overcome the ‘curse of dimensionality’ but also findeconomical and technically sound generation planning scheme.