Biomass lycium chinensis stalks were used as raw materials，KHCO₃ as activator，and urea as nitrogen source to explore the preparation of nitrogen-doped biochar.The morphology，structure，and surface functional groups of the produced biochar were characterized was performed using scanning electron microscopy（SEM），nitrogen adsorption-desorption instrumentation（BET），X-ray powder diffraction（XRD），Raman spectroscopy（Raman），Fourier transform infrared spectroscopy（FT-IR），and X-ray photoelectron spectroscopy（XPS）.And its adsorption behavior towards methylene blue（MB） in water was explored.The results showed that the optimal conditions for KHCO₃ to activate Lycium chinensis stalks were as follows：mass ratio of 1∶2（Lycium chinensis stalks carbonized material and KHCO₃），activation temperature of 800 ℃，and activation time of 1 h.The optimal conditions for doping urea on the surface of lycium chinensis stalks biochar（LBC） were as follows：mass ratio of 1∶4（LBC and urea），and nitrogen-doped biochar（LBC-N） was prepared by calcination at 800 ℃ for 1 h.The specific surface area of LBC and LBC-N were 940.29 m²/g and 1 169.78 m²/g，the total pore volumes were 0.57 cm³/g and 0.72 cm³/g，and the average pore sizes were 5.81 nm and 3.20 nm，respectively.All of them were mainly mesoporous biomass activated carbon materials.Under the corresponding experimental conditions，the adsorption capacities of LBC and LBC-N for MB were 542.02 mg/g and 639.20 mg/g，respectively.The Pseudo-second-order model，Intra-particle diffusion model and Langmuir isothermal model could well describe the adsorption process of MB by LBC and LBC-N.According to the physicochemical properties and adsorption experiments of nitrogenous biochar，the adsorption process of LBC-N on MB molecules was mainly a result of π-π interaction，hydrogen bonding，electrostatic attraction and other chemical effects，and the synergistic effect of physical adsorption by pore filling.