Decision-making of cooling and heating source schemes of air-conditioning system involves of a great deal of the latest data about air-conditioning products. Meanwhile, designers also need to consider several factors including overall investment, energy consumption, operation maintenance, performance reliability and environmental protection. An internet-based decision-making system of air-conditioning cooling and heating source is proposed. The paper discusses programming design of dynamic webpage and active serve pages (ASP), and studies the establishment and usage of network data base. Grey optimization model is constructed for determination of the best cooling and heating source scheme considering the multi-factors. A practical case is analyzed demonstrating the validity of the method. Internet-based decision-making system applying grey optimization method might be useful in cooling and heating source selection.