In order to prepare low expansion, high strength and light weight composites, ZrW2O8-Cf/E51 composites were prepared by compression molding method, and the effects of ultrasonic time on its microstructure, thermal expansion behavior and ultimate tensile strength were studied. The results show that the agglomerated particles will be blocked by the fibers and gather on the surface of fiber bundles during the preparation. Within 20 minutes, the agglomeration of ZrW2O8 particles can be reduced by prolonging the ultrasonic time. With the decrease of particle agglomeration, the fracture surface of the composites will be changed from plane without fiber pull-out to uneven with fiber pull-out. During the thermal expansion process, the dL/L0of ZrW2O8-Cf/E51 composites show three stages: increase, decrease and slow increase under the combined action of carbon fiber and ZrW2O8 particles. When ultrasonic time increases from 5 min to 20 min, the average thermal expansion coefficient of ZrW2O8-Cf/E51 composites decreases by about 130%, and the ultimate tensile strength increases by about 8%.