Si-O-C aerogels were prepared based on the precursor conversion method by adjusting the molar ratio of methyitrimethoxysiiane (MTMS) and deionized water. The carbon fiber matrix composites were obtained after the aerogels were impregnated with carbon fiber preforms and dried. The effects of the molar ratio of methyitrimethoxytiiane and deionized water on the properties of aerogels were studied by XRD, SEM, FT-IR, mechanical properties and thermal conductively analysis, and the effects of pyrolysis treatment on the properties of carbon fiber matrix composites were analyzed. The results showed that the adhesion between Si-O-C aerogel and carbon fiber prepared by precursor conversion method was high. With the increased of the ratio of n (MTMS) : n (deionized water), the integrity of the aerogel increased and the number of cracks decreased, and the compressive strength of the composite showed a trend of increasing at first and then decreasing. When n (MTMS) : n (deionized water) = 1 : 50, the maximum compressive strength of the composite was 1.595 MPa, the maximum stress at the elastic deformation stage was 0.95 MPa, and the minimum thermal conductively was 0.0198 W/(m K).The pyrosis at 1000 °C promoted the conversion of Si-O bond to Si-C bond in carbon fiber matrix composites, resuming in the increase of Si-C bond, but the pyrolysis caused cracks on the framework and surface of the aerogel, and when n (MTMS) : n(deionized water) = 1 : 50, the deformation resistance of the compose as the best. [ABSTRACT FROM AUTHOR]