Silicon carbide whiskers (SiCw) has many excellent properties such as high strength, high elastic modulus. SiCw was dispersed by using water reducer as dispersant in order to modify cement-based composites. Through 8-shaped method, ring tests of crack resistance, and three-point bending test with pre-cracks based on the digital image correlation method, the fracture properties of materials were measured. The pore structure was studied by mercury intrusion porosimetry and the microstructure was observed by SEM to analyze its enhancement mechanism on cement-based composites. The results show that the SiCw causes crack deflection during crack propagation. By crack path analysis, the crack path of SiCw modified cement-based composites is more tortuous and consumes more energy while crack propagation than the blank group. The incorporation of SiCw helps to improve the brittleness of cement-based composites and provides new ideas for improving the performance of cement-based composites. The SiCw bridging effect and pull-out mechanism effectively control the crack propagation, thus enhancing the crack resistance and the tensile strength of the cement-based materials. From the perspective of pore structure, there is no obvious filling effect after SiCw incorporation. The addition of SiCw increases the total porosity of cement mortar slightly, which has no adverse effect on tensile strength and fracture thoughness.