The relation among electronic structure, chemical bond and property of Ti_3SiC_2 and Al-doped was studied by density function and discrete variation (DFT-DVM) method. When Al element is added into Ti_3SiC_2, there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti_3SiC_2, adding a proper quantity of Al can promote the formation of Ti_3SiC_2. The density of state shows that there is a mixed conductor character in both of Ti_3SiC_2 and adding Al element. Ti_3SiC_2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al. The relation among electronic structure, chemical bond and property of Ti_3SiC_2 and Al-doped was studied by density function and discrete variation (DFT-DVM) method. When Al element is added into Ti_3SiC_2, there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti is somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before Therefore, in preparation of Ti_3SiC_2, adding a proper quantity of Al can promote the formation of Ti_3SiC_2. The density of state shows that there is a mixed conductor character in both of Ti_3SiC_2 and adding Al element. Ti_3SiC_2 is with more tendencies to form a total number of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.