Tar measurement and calculation is crucial for understanding the in-situ tar elimination and hydrogen-rich syngas production during the biomass gasification process. In this study, the method of evaluating tar production was proposed and studied on a two-stage fixed-bed reactor. Two different groups of oxidized and reduced oxygen carriers were investigated for comparison. The collected tar was tested on a gas chromatography mass spectrometry (GC-MS) system. The types of the tar were all belonged to aromatic hydrocarbons. The H-2 composition in the syngas was over 34% in three reduced-OC conditions. The carbon percentage identified by the GC-MS was at the range of 93.75-95.05 wt%. The average carbon from the char combustion period was 2.85 mmol. The tar yield in the three oxidized-OC conditions was 43 +/- 22 mg/g, 53 +/- 11 mg/g, and 62 +/- 8 mg/g, respectively. The result indicated that the reduced OC had a catalytic effect for increasing the H-2 composition in syngas. On the other hand, the oxidized OC influenced the reactions by providing with lattice oxygen. The evaluation of the produced tar was beneficial for a further understanding of the mechanism for producing the H-2-rich syngas. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.