This study presented an approach to upgrade the qualities of pyrolysis products based on hammer-(screen size 1 mm)and rod-milled(Rod-milling for 60 min), combination hammer-and rod-milled and torrefaction(250 degrees C for 30 min). The pyrolysis of raw and pretreatment wheat straw were performed in a fixed-bed pyrolysis reactor at 500 degrees C for 15 min. The mechanism of the yields and qualities of pyrolysis products changes was deeply analyzed. Results indicated that particle size, crystallinity cellulose, and morphological structure were the main factors affecting pyrolysis processes. Rod-milled and torrefaction pretreatment have an extremely important effect on the yield, properties, and energy distribution of pyrolysis products. Interestingly, combined rod-milled and torrefaction pretreatment improved the distribution and maximized the qualities of pyrolysis products. Compared with other pretreatments, combined rod-milled and torrefaction pretreatment produced the non-condensable gas with the highest higher heating value of 12.03 MJ/Nm(3), the bio-oil with the lowest water content and acidity of 43.63DM.% and 2.39 KOH.mol/g. Moreover, under combined rod-milled and torrefaction pretreatment, the specific surface area and pore volume of pyrolysis bio-char increased significantly compared with others. Overall, combined rod-milled and torrefaction pretreatment is a promising pretreatment method for the preparation of high qualities biomass fuels. (C) 2019 Elsevier Ltd. All rights reserved.