Several combined heat and power (CHP) system options are presented to assess and compare with respect to the end users' requirements. According to the obtained data from literature, 16 kinds of CHP systems are evaluated using gray relational method in multi-criteria, such as technology, economy, environment, and society. The results depend greatly on the criteria weights in multi-criteria evaluations. Aiming to obtain rational result, this paper reviews the weighting method briefly and proposes an optimal combined weighting method to consider the subjectivity of decision-maker and the objectivity of measurement data. The singular value decomposition aggregation method is employed to verify the rationality of evaluation result. Through multi-criteria evaluation and discussions, the combination weighting method is recommended to be used in the selection of CHP schemes. Finally, the best CHP system is selected and the most conspicuous factors having great impact on CHP system with respect to the users' requirements are given out. Copyright (C) 2009 John Wiley & Sons, Ltd.