In this paper, the effects of pyrolysis temperature, microwave power, moisture content and additive on H-2 yield is investigated. The feedstock is rice straw, which is the commonest crop straw. And a four-factor four-level orthogonal experiment is designed to reveal the rank of these factors and the optimal pyrolysis condition. The result shows that: when pyrolysis temperature and microwave power increased, H-2 yield (vol.%) first increased and then decreased; when moisture content increased, H-2 yield decreased; without additive, H-2 yield was 36.14% which is the highest. The rank of four factors is moisture content, additive, pyrolysis temperature and microwave power. When the pyrolysis temperature was 700 degrees C, the microwave power was 2.5 kW, the moisture content was 61.84% and ZnCl2 was used as the additive in microwave-assisted pyrolysis of the rice straw, a high H-2 yield of 44.94% was achieved. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.