The comprehensive utilization of renewable energy and clean fossil fuel contributes to improving the stability of energy supply system and reducing environmental impact. Therefore, a bio-gas and natural gas co-firing in combined cooling, heating and power (CCHP) system based on ground source heat pump is presented and modeled using exergetic and exergoeconomic methods. The exergy and exergy cost flows of CCHP system are presented under three different gas mass ratios and the influences of some key parameters (biomass and natural gas cost, interest rate, service life and operating time coefficient) on unit exergy cost of products are also analyzed. The results indicate that the introduction of natural gas improves the exergy efficiency; when the gas mass ratio varies from 0 to 1.0 the unit exergy cost of electricity generated by gas turbine, chilled water and hot water decrease from 11.26 $/GJ, 92.21 $/GJ and 69.92 $/GJ to 3.84 $/GJ, 43.52 $/GJ and 23.73 $/GJ, respectively. Furthermore, the sensitivity analysis shows that unit exergy cost of products increases with the increasing of biomass cost, natural gas cost and interest rate; while decreases non-linearly with the increasing of service life and operating time coefficient. The proposed CCHP system provides an idea for other hybrid renewable energy system, and exergoeconomic methodology shows a better understanding of complex energy system performance in terms of both exergy and economic aspects.