The simulation model for the long-term planning of energy system development is designed for the long-term planning of energy system of state, for the period from approximate 30 years. The analysis results of model we can use for the long-term plan of energy system development of the state. The model is divided in three basic parts and his application supposed the use of the adequate model for planning the long-term development of electrical power system for the long-term consumption of electricity by the minimal production costs. These three sub-models of the model for the long-term planning of energy system development are the model for calculation the energy flows, the model for calculation the costs in the energy system and model for calculation the investments in the energy system. In the sub model for calculation of the energy flows in the energy system of the country, calculation starts from the forecasted useful energy for some consumer groups, respectively from the forecasted final energy demand for that consumer groups and for that aims of energy consumption where the substitution is not possible or where the conversion factors to the useful energy are similar or equal, independent of used energy form. When all calculations for the final energy consumers are carrying out the quantities of all energy forms for energy and non-energy needs are determined. The next step in the calculation is the determination of the total final demand for all energy forms that are taking part in the supply of final energy consumers. The final consumption of transformed energy forms is the basic input data for calculation the energy opportunities in the energy transformation plants. On the basis of the final demand of transformed energy forms and on the basis of the consumption of transformed energy forms as input energy in the some energy transformation plants for the energy transformation process, the model determine the structure of input energy in all energy transformations plants, as well as the structure of transformed energy production also in all energy transformation plants. The calculation carried out for the final energy consumers and calculation carried out for the energy transformation plants are the basis for the construction of energy balances, as the main result of energy flows calculation. To be able make the individual energy balances for all energy forms and complex energy balance of the total energy system, it is necessary to realize some more analysis and calculations. It is worked out the analysis of possible production of primary energy forms, calculation of the necessary energy consumption for the energy sector own use and calculation of the losses for that energy forms which are transported and distributed to the consumer using energy networks.In the sub-model for the costs calculation of energy system, the calculation of the costs for all energy forms and for all plants of energy system is carried out, on the basis of calculation carried out in the sub-model for calculation of the energy flows and on the basis of other data. The other data necessary for the cost calculation are the investment cost, the economic lifetime, the long-term discount rate, the capacity of plant, the fixed operating and maintenance costs, the variable operating and maintenance costs and the costs for the energy or for some other input in the energy plant. The costs of the oil refineries, natural gas liquids plant, the public cogeneration plants, the industrial cogeneration plants and small cogeneration plants have been determined on the specific way. The investments to the energy system are calculated in third sub-model of simulation model for the long-term planning of energy system development. The investment calculation is divided in the three parts. In the first part of sub-model the investments necessary for the production of primary energy are calculated, in the second part of this sub-model the investments to the plants for the energy transformations are calculated and in the third part of sub-model the investments in the energy networks are calculated.