The enhancing effect of calcium oxide (Can) addition on steam gasification of four typical Chinese agricultural biomass wastes for H-2 production has been investigated in an atmospheric fluidized bed reactor under different conditions. The result indicates that CaO acts.both a CO2 absorbent and a catalyst in the gasification process. Its addition significantly increased the concentration and yield of H-2 and simultaneously decreased the content of CO and CO2 in the product gas. At lower temperature (550-650 degrees C), the CO2 absorption enhancing effect of CaO greatly promoted the gasification process to produce a product gas with high content of H-2 and low CO and CO2. While at higher temperature (700-800 degrees C), the catalytic effect of CaO became significant, the cracking of pyrolytic volatiles and steam gasification of volatiles and char as well as WGS reaction were intensified, which also caused the increase in H-2 yield in spite of the decrease in H-2 concentration. The increases of molar ratio of CaO-C (CaO/C, 0-2) and mass ratio of steam to biomass (S/B, 0.8-2) were both beneficial for H-2 production process. CaO addition showed limited effect on CH4 and C2+ even at high temperature and high mass ratio of steam to biomass. The type of biomasses is closely associated with H-2 yield, which is closely related to the volatile and C content of biomass materials. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.