Nitrogen fertilizer was excessively applied in the agricultural production, which resulted in soil secondary salinization and deterioration. Biochar has been gradually applied in soil restoration due to adsorption capacity. However, solanaceous vegetables straw-derived biochar was rarely reported. The present study aimed to explore the effect of solanaceous vegetables straw-derived biochar on adsorption of nitrate nitrogen and mitigation of soil secondary salinization. Straws of sweet pepper, tomato and eggplant were prepared as biochar by pyrolysis. Adsorption and mechanism for nitrate nitrogen removal by experimental solanaceous vegetables straw biochar was examined. Surface morphology and functional groups were characterized by scanning electron microscopy (SEM) and Fourier transform near-infrared spectroscopy (FTIR). The adsorption process of nitrate nitrogen was simulated and fitted by kinetic model and isothermal adsorption model. The adsorption mechanism of biochar was analyzed according to morphology and model parameters. All of the experimental solanaceous vegetables strawderived biochar showed adsorption capacity of nitrate nitrogen. The maximum adsorption capacity of eggplant, tomato and sweet pepper straw-derived biochar were 114.788mg/g, 29.736mg/g and 9.759mg/g, respectively. The adsorption processes of eggplant and sweet pepper straw biochar were well fitted by quasi-second-order kinetic model, which was controlled by the integrated adsorption of chemical bond, micro-porefilling and internal diffusion. The adsorption process of tomato straw biochar was well fitted by the quasi-first-order kinetic model, which was mainly physical adsorption. Functional groups such as hydroxyl group, methyl group, methylene, carboxyl group and carbonyl group were observed in experimental biochar, according to FTIR analysis. Additionally, ether bonds were observed in eggplant and sweet pepper straw biochar and alcohol hydroxyl groups were observed in tomato straw biochar. Therefore, adsorption capacity of nitrate nitrogen was observed in the experimental solanaceous vegetables straw biochar. The eggplant straw biochar had the greatest adsorption capacity of nitrate nitrogen, which was affected by various physicochemical mechanisms such as pore filling, functional groups and complexation. The results demonstrated that eggplant straw biochar had great potential in amendments of secondary salinization soil. The present study provided insight into the effective utilization of solanaceous vegetables straw and soil remediation in crop production.