Abstract: Using sunflower stalk as the main raw material and KOH solution with a mass fraction of 10% as the dipping agent, biomass charcoal was prepared under 350℃ and 410℃, respectively. The properties and structures of raw materials and biochar were characterized by thermogravimetric analysis, infrared spectroscopy and Raman spectrometer. The results showed that the maximum weight loss rate of sunflower stalk was 80%, thermogravimetric rate reached the maximum at 308℃, the degradation rate decreased at 439℃ and started carbonization and dealkylation and aromatization condensation polymerization. The types of functional groups of biochar prepared at the two temperatures were basically the same. The degree of aromatization and graphitization of biochar prepared at higher temperatures was higher, which was conducive to enhancing the chemical stability of biochar.