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The shortcomings such as high water content, low energy density and difficulty to storage, have limited the large-scale applications of agricultural straw. The torrefaction characteristic of four typical straws in China such as rice straw, cotton stalks, corn stalks, wheat straw, was investigated, which was carried out in the fixed-bed reactor and focused on the evolution of physical and chemical properties of straw during torrefaction. After torrefaction, the apparent volume of agricultural straw was significantly reduced and a more uniform distribution of particle size was observed which suggested the grinding performance could be significantly improved. Meanwhile, the number of solid oxygen-containing functional groups in the solid product reduced. The significantly increasing of the fixed carbon content and the significantly decreasing of the oxygen content improved the heat value of solid products. Although the mass and energy production yield ratio decreased after torrefaction, the energy production yield ratio was better than the mass. The torrefaction was benefit to the improvement of energy property and material characteristics of straw and had a positive effect on the quality of biomass material.