Combined Cooling, Heating and Power (CCHP) systems are safe, efficient, and environmentally friendly systems, which have been widely used all over the world. However, the greenhouse gas emission problems of CCHP systems have not been fully studied. This research adopted a multi-product carbon footprint (MPCF).method to assess the greenhouse gas emissions of a CCHP system. Activity data, mass and energy balances were checked to ensure the accuracy of the assessment. To solve the allocation problems, the authors introduced the concept of carbon footprint contribution rate, x(j), and presented an applicable expression of xj for CCHP systems. The MPCF calculations showed that without optimization the total MPCF of the CCHP system is 8.071 kg-CO(2)e/kW h-prod and direct MPCF occupies the carbon footprint overwhelmingly. Moreover, an optimization thought that MPCF can be decreased by increasing the amount of cooling output was proposed theoretically. To corroborate the thought, a dehumidifier unit has been incorporated into the original CCHP system. Compared with the original system, results show that the MPCF of the optimized CCHP system drops by 7.5% while the total carbon emissions rise only by 0.5%, which means the CCHP system after optimization can produce more products than before but only with a small increase of environmental costs. (C) 2015 Elsevier Ltd. All rights reserved.