The article uses carbon fiber (CF) to prepare CF reinforced polycarbonate/acrylonitrile-butadiene-styrene copolymer (PC/ABS) composites, and studies the influence of CF on the mechanical and thermal properties of PC/ABS composites, in order to obtain the optimal content of CF. Mechanical property analysis shows that as CF increases, the tensile strength and flexural strength of CF reinforced PC/ABS composites continuously increases, while the impact strength first increases and then decreases. Thermal property analysis shows that with the continuous addition of CF, the heat deflection temperature of CF reinforced PC/ABS composites continues to increase, and the melt flow rate (MFR) first increases and then decreases. When the CF mass frction is 15%, the comprehensive mechanical and thermal properties of CF reinforced PC/ABS composites are optimal. Compared with the material without CF, the tensile strength, flexural strength, and impact strength are increased by 134.7%, 133.3%, and 69.6%, respectively, the heat deflection temperature is increased by 39 ℃, and the MFR is increased by 27.8%.