A new adsorbent CaCO3/g-C3N4 was successfully synthesized using melamine and calcium carbonate. The structure of CaCO3/g-C3N4 was studied in depth through XRD, FT-IR, SEM, TEM and BET. The experimental results show that CaCO3/g-C3N4 has fast and efficient selective adsorption performance (89.34%) and excellent adsorption capacity (1 209.75 mg/g) for crystal violet (CV). Adsorption kinetics and isotherms show that CaCO3/g-C3N4 adsorption of CV follows the quasi-second-order kinetic model and the Langmuir isotherm, respectively. At the same time, based on the FT-IR and XPS spectra before and after adsorption and experimental conclusions, a reasonable adsorption mechanism was proposed. The synergistic effects of π-π stacking, n-π interaction, and hydrogen bonding are important reasons for the selective adsorption of CV by the CaCO3/g-C3N4.