As energy demands around the world increase, the need for renewable energy sources, such as Micro-Grid (MG) that will not harm the environment has been increased. Micro-Grid has been extensively investigated as a promising solution to energy challenges in 21st century. The optimal generation is one of the important functions for the Micro-Grid operation. It should be noted that supplying thermal load with combined heat and power systems is one of the most evident features of the Micro-Grids which increase the efficiency of the system. In this study, the operation of Micro-Grids by considering two kinds of state i.e. isolated and connected is investigated and the results for these different states are compared together. In addition, the effect of CHP systems in a Micro-Grid and the possibility of collaboration of Micro-Grid in power supply marketing is studied. The results indicate that existences of CHP systems leads to reduction of operating cost; consequently, consumers pay less for energy. So this proposed model is used to reduce the total operating costs. The equations of Micro-Grids are solved using the mathematical analysis which is based on the application of Mixed Integer Programming (MIP).