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• The removal rate of Ca and Mg by hydrochloric acid washing was above 97 %. • Acid washing affected the pyrolysis behavior of corn straw. • Acid washing obviously reduced the activation energy value of the main reaction zone. • Pretreatment significantly influenced bio-oil composition and distribution of corn straw. • More value-added chemicals could be obtained by hydrochloric acid washing. Corn straw was washed using hydrochloric acid in this study. The properties of biomass and pyrolysis characteristics and the bio-oil components were examined systemically. The results showed acid washing removed the most metals in corn straw, improved the contents of cellulose and hemicellulose and reduced the activation energy of pyrolysis process. FTIR (Fourier transform infrared) spectra displayed some differences in peak transmittances between the original and pretreated corn straw. The GC–MS (Gas chromatography-mass spectrometer) analysis showed the major oxygenated components in bio-oil including furans, ketones, acids, phenols and aldehydes were efficiently destroyed by hydrochloric acid pretreatment, while the alcohols and sugars content increased significantly. A significant decrease of furans content was observed, especially the benzofuran, 2,3-dihydro-, from 7.23 % to 0%. D-allose and D-Erythro-Pentose, 2-deoxy- have been found in pretreated corn straw, which implied that more value-added chemicals could be obtained by hydrochloric acid washing. [ABSTRACT FROM AUTHOR]