Three kinds of C/C composites with density of 1.70 g/cm ³, 1.82 g/cm ³ and 1.89 g/cm ³ were prepared. The materials employing needled preform were densified by chemical vapor deposition and pitch impregnation-high pressure carbonization (HPIC) process. The density was controlled by times of HPIC. The results showed that the tensile strength decreased with the increasing density. When the density was low, bonding strength of interface between fiber and matrix was low which could delay the fracture of fiber and increase the tensile strength, the tensile fracture of sample possessed the characteristic of pseudo-plastic fracture. Consisted with the shear strength, the compress strength rose and then fell with the increase of density. With the increasing density, the expansion coefficient increased. Interstices among microcrystals absorbed a little amount of expansion during heating process, therefore, the fall of density was beneficial to the decrease of expansion coefficient of C/C. With the increasing density, the thermal conductivity coefficient increased obviously, and microcrystals enlarged which contribute to the transfer of vibration of crystal lattice and increase of thermal conductivity coefficient. The factor of thermal stress rose and then fell with the increasing density. The C/C with the density of 1.82 g/cm ³ possessed high thermal shock resistance as thermal structure components. In the course of C/C R&D, the density target can be designed according to synthetical demands of mechanical and thermal properties.