Steam gasification of pine sawdust over hematite was carried out in a decoupled dual loop gasification system. The system is composed of two parts, i.e. a fluidized bed gasifier and a moving bed reformer. Two parallel loops based on the above two parts were set up followed by a particles grading cyclone. The bed material in gasification loop was fine quartz sand while that in the reforming loop was the mixture of coarse hematite and quartz sand. The ratio of hematite to biomass, reforming temperature and steam to carbon ratio (S/C) were investigated. The results show that the above factors play crucial roles in biomass steam gasification. Higher reforming temperature promotes tar removal and water conversion while higher S/C increases H-2/CO ratio and dry gas yield. At gasification temperature 750 degrees C and reforming temperature 700 degrees C, the tar yield of 4.2 g/Nm(3) and 29.6 g/Nm(3) have been obtained with hematite and quartz sand as bed material, respectively.