Biochar adsorption emerges as a convenient and cheap treatment technology to cope with the metal pollution in wastewater. In this study, a biochar made from corn stalks was prepared and its adsorption characteristics for two heavy metals, Pb and Cd, were investigated by materials characterization and batch experiments. Biochar pyrolyzed from waste corn stalks at 400–600 °C, where biochar prepared at 600 °C (BC600) was used to perform following experiments. In materials characterization, the SEM images were initially used to reveal an obvious porous structure feature of corn stalk biochar, followed by XPS and FT-IR analyses unraveling the effects of functional groups in adsorption, especially for phenol and carboxyl groups. These functional groups provided vital adsorption sites. In batch experiment, batch experiments were conducted under different factors such as pH, temperature, and background ionic strength. The increase of pH and temperature can improve the adsorption capacity, whereas the ionic strength showed negative effects. The adsorption processes of both metals can be interpreted by fitting pseudo-first order model, as indicated in kinetic experiments, and the adsorption isotherm can be well described by the Langmuir model. Overall, this study revealed the characteristics of corn stalk biochar and deciphered the potential adsorption mechanisms.