Abstract: Joining of pressureless sintered SiC was carried out by the reaction joining process using the mixture of hydrogen-containing polysiloxane and vinyl-containing polysiloxane (denoted by HPSO-VPSO) with additive Al-Si powders as joining materials. The pyrolysis of HPSO-VPSO with Al-Si powders was studied by thermogravimetry, differential scanning calorimetry and X-ray diffraction. The effects of the joining temperature, the content of Al-Si powders and the heating rate on the joining strength of joints were investigated. The microstructure and composition of interfacial area were analyzed by scanning electron microscopy and energy dispersive spectrometry. The results show that the additive Al-Si powders promote the pyrolysis of HPSO-VPSO and lead to the increase of the ceramic yield per unit HPSO-VPSO. The maximum shearing strength of the joints is obtained to be 93MPa at the joining pressure of 50kPa, the joining temperature of 900℃, the holding time of 30min, the heating rate of 4℃/min and the Al-Si powders mass fraction of 50%. Microstructure study reveals that the thickness of the interlayer is about 75μm, and the contact at the interfaces is intact without obvious pores and cracks. The interdiffusion of Al and Si takes place at the interfacial area, which contributes to the interfacial bonding, resulting in the increase of the joining strength of the joints.