Abstract: To quickly and accurately detect the elastic modulus of the reactive bonded silicon carbide (RBSC), the pulse-echo method was used to detect the ultrasonic longitudinal wave velocity and shear wave velocity of RBSC of different densities based on the relationship between the ultrasonic wave velocity and elastic properties of the material. The elastic modulus of the material was further obtained by the density calculation. The direct model between the elastic modulus and the density was firstly established. As long as the density of RBSC was known, the elastic modulus can be rapidly and directly used to predict its elastic modulus value. To verify the reliability of the model, this paper compared the predicted values of the model with the measured values and the values obtained by the traditional empirical model. Furthermore, the relationship between the areal porosity and free silicon content of RBSC with different densities was investigated and an empirical formula of the density and the free silicon volume percentage content was established. Results showed that the elastic modulus prediction model established in this paper can not only obtain the elastic modulus value of RBSC quickly but was also conducive to the adjustment of the RBSC preparation process, combining with empirical formula of the density and the free silicon volume percentage content. It is important for the development and detection of composite materials such as silicon carbides.