Abstract: In order to reveal the regulation mechanism of P factor on the mass concentration of chemical composition in prehydrolysis liquor of lignocellulose, the mass concentration changes of solid content, lignin, xylose and glucose were studied at different prehydrolysis temperature(170-210℃) and time(30-120 min). The results showed that the mass concentration of solid content, lignin and glucose gradually increased with the increase of prehydrolysis temperature and time. While the mass concentration of xylose rapidly decreased with the increase of temperature and prehydrolysis time at 190℃. There was a regulation effect of P factor on mass concentration of chemical composition in prehydrolysis liquor of poplar. The mass concentration of solid content, lignin and glucose presented an exponential increase with the increase of P factor. However, a conspicuous decrease of mass concentration of xylose was found with the increase of P factor when P factor < 3 300.