Abstract: Biomass steam gasification is a promising technology for hydrogen-rich gas production. In this paper the decoupled triple bed gasification (DTBG) system has been proposed. The system is composed of 3 decoupled reactors, i.e., gas-solid countercurrent moving bed pyrolyzer, radial-flow moving bed reformer and riser-type combustor. The steam was used as gasifying agent and the calcined olivine was used as circulating heat carrier and in-situ tar destruction catalyst as well. Experiments have been conducted at a pyrolyzer temperature of 700 ℃, a combustor temperature of 850 ℃ and the ratio of steam mass to biomass mass (S/B) of 0.65. The influences of biomass type on the gasification performance were investigated with saw dust, rice husk, wheat straw and cotton stalk as biomass feedstock at the reformer temperature of 800 ℃. The effects of reformer temperature (700-850 ℃) and biomass feeding rate (120-220 g/h) on gas yield, tar content, gas composition, carbon conversion as well as gasification efficiency were investigated with saw dust as feedstock. Besides, the characteristics of gasification tar at the varied reformer temperatures were investigated using gas chromatograph. The results indicated that the volatiles of biomass have great effect on the gasification performance. The gas yield, carbon conversion, the concentration of H2 and CO increased and CO2 concentration decreased with increasing volatile matter content of biomass. In the DTBG system, the pyrolyzer and reformer are separated and the volatiles released from pyrolyzer were the main source of the product gas. Therefore, a secondary reaction of volatiles in reformer with the presence of the olivine, such as steam reforming reaction, tar creaking reaction, plays a critical role in determining product gas composition as well as gas yield. The saw dust was found to be preferable biomass type for hydrogen-rich gas production. Gas yield increased from 0.91 to 1.08 m3/kg while tar content decreased from 19.1 to 7.3 g/m3 at the reformer temperature range of 750-850 ℃. At the same time, carbon conversion and gasification efficiency were dramatically increased from 71.4% to 81.4% and from 56.4% to 65.2%, respectively, with increasing reformer temperature from 750 to 850 ℃. The H2 concentration increased and CO2 concentration decreased with the increasing biomass feeding rate, which yet had little impact on tar content. Specifically, product gas with the H2 concentration of 42.2%, CO concentration of 14.6% and the tar content of 10.1 g/m3 has been obtained at the reformer temperature of 800 ℃ and biomass feeding rate of 220 g/h. The gasification tar was basically composed of naphthalene, biphenyl, acenaphthene, dibenzofuran, fluorene, phenanthrene, fluoranthene, and pyrene, in which naphthalene was found to be the dominate component. Single ring hydrocarbons were totally destructed and 3-4 ring PAHs (polycyclic aromatic hydrocarbons) decreased, while the concentration of naphthalene was dramatically increased from 54.7% to 75.6% at the reformer temperature range of 750-850 ℃. It can be demonstrated that the novel design of reformer in the DTBG system with olivine not only is favorable to increase tar reforming/cracking reactions which favors tar removal, but also appears as a feasible technology for hydrogen-rich gas production. This work is expected to be helpful for the design, operation and optimization of large-scale gasification plant.