Combined adsorption and oxidation using biochar to activate persulfate has been recently applied to remove contaminants, yet most of the experiments are carried out using artificial synthetic water instead of real waters. Here we tested the removal of humic substances which is abundant and affecting water quality in natural waters, by persulfate combined with corn stalk biochar. Results showed that, compared with biochar prepared at 400 °C, 600 °C and 700°C, biochar prepared at 900 °C after modified by hydrochloric acid had greater specific surface of 459.260 m2/g, richer porosity and higher removal of humic acids of more than 80% at pH 5.0-9.0 in pure water. Treatment of real river water showed decrease of 80.4% and 69.7% of total organic carbon (TOC) and UV 254 , respectively. The addition of tert-butyl-alcohol (TBA) and methanol (MeOH) inhibited the removal to a certain extent suggesting the existence of •OH and SO4−•. It was speculated that in addition to the adsorption of biochar, the oxygen-containing functional groups on its surface might act as active sites to promote the production of oxidized species. This work provides a method for corn stalks utilization in accordance with environmental sustainability and resource recovery.