Based on density functional theory with spin-orbit corrections included, the electronic structures of diadochic compounds Bi2Te3-xSex(x≤3) have been calculated by first-principles full-potential linearized augmented plane-wave method. The calculated results indicate that spin-orbit interaction is crucial in understanding the gap structure near the Fermi energy. Bi2Te3-xSex(x≤3) are indirect-gap semiconductors, and there is a saddle point at the Γ point. The density of states near Fermi level mainly consists of p orbitals of each atom. For the chemical bonding of the various layers of atoms, the covalence bond component of X(1)—Bi is stronger than that of X(2)—Bi (X=Te, Se). With the increase of the Se mol ratio in the systems, the unit cell volume is reduced, the energy of the system is increased, and the covalence bond component of Te(1)—Bi, Se(2)—Bi, Se(1)—Bi is gradually enhanced.