The work aims to prepare modified microfibrillated cellulose from broad-leaved pulp and use it to enhance acrylonitrile-butadiene-styrene (ABS). The broad-leaved pulp was dissociated into microfibrillated cellulose (MFC) by co-grinding with Ca (OH)2 as grinding aid and swelling agent, and then modified by carbonization and sodium stearate to obtain calcium stearate-coated microfibrillated cellulose (CS-MFC). Then, CS-MFC was added to ABS in different proportions by solvent casting method, and CS-MFC/ABS composites were prepared by twin-screw mixed extrusion and vulcanizing machine pressing method. The properties of MFC, CS-MFC and CS-MFC/ABS composites were measured. The calcium hydroxide had a significant grinding aid effect and the calcium stearate in the obtained CS-MFC was coated on the surface of MFC by physical adsorption, and the water contact angle increased from 18.2° to 72.3°. CS-MFC was added to the ABS matrix and when the addition amount of CS-MFC was 5%, the tensile strength of the composite reached 38.0 MPa, an increase of 15.5%. When the addition amount was 10%, the elastic modulus reached 1.72 GPa, an increase of 5.5%. CS-MFC had little effect on the thermal stability of ABS. The CS-MFC obtained by co-grinding and sodium stearate modification can effectively improve the tensile strength and elastic modulus of ABS, which is conducive to improving the application performance of ABS.