The relations among structure property and chemical bond of TiC,TiN and TiO ceramics,as well as Nb doped TiC,are studied with SCF Xα DV,one of the quantum chemistry calculating methods.The calculated results are consistent with the experimental results that the hardness and strength are in the order of TiC > TiN > TiO,and when Nb element added to TiC increases,the vacancies being in short of C atom increase,hardness and resistance of the series samples of (Nb_yTi_1-y)C_x decrease correspondingly.