SiC matrix was obtained by sintering polycarbonsilane at 800， 1 000， 1 200 ℃， and the effect of temperature on the density and crystallization degree of SiC was studied. With the increase of temperature， the crystallization degree， the density of the matrix and the proportion of Si increases. At 800 ℃， the density of the matrix is 2.30 g/cm³， and the matrix structure is close to the amorphous state . At 1 000 ℃ and 1 200 ℃， the densities of the matrix are 2.50 and 2.56 g/cm³ ， and the grain sizes are 2.6 and 4.1 nm， respectively. C/SiC composites are prepared by PIP process with polycarbosilane as precursor and carbon fiber fabric as reinforcement， the maximum pyrolysis temperatures in the whole pyrolysis process are also 800 ， 1 000 and 1 200 ℃. The effect of matrix structure on the mechanical behavior of the composites is studied by mechanical properties test and microstructures observation. The results show that increasing the pyrolysis temperature in a certain range is beneficial to improve the properties of the matrix and the matrix’s densification efficiency ，which make the mechanical performance of the material improved， and especially has obvious effect on improving the bending strength ， interlaminar shear strength and compression strength of C/SiC composites.