Co-gasification of coal and biomass has many merits with regards to feasibility in fuel supply and synergetic catalytic effect. In this paper, the influence of biomass on energy and element utilization efficiency during co-gasification is studied to further reveal the essence of the synergistic effect. Coal gasification, biomass gasification and the co-gasification were all performed in the same fluidized-bed reactor. It was found that the dry gas yield, the cold gas efficiency and the carbon conversion efficiency all increased with an increase of both biomass ratio (BR) and gasification temperature. The co-gasification temperature and the amount of water in the co-gasification process were seen to decrease with an increase of BR when keeping the H-2/CO ratio as a fixed value. The elements utilization efficiency of carbon (C_EUE) and oxygen (O_EUE) were increased with the increase of BR while hydrogen element utilization efficiency (H_EUE) was decreased. H_EUE, O_EUE and C_EUE increased as the gasification temperature was increased, but O_EUE was observed to decreased when there was an increase in the steam flowrate and BR. H_EUE and C_EUE are optimized with an increase in the oxygen equivalent ratio. (C) 2013 Elsevier B.V. All rights reserved.