To improve the thermoelectric performance of n-type BiSbSe3, the cation and anion codoping was implemented by doping SnCl4. SnCl4 doping mainly regulate the relationship between electrical conductivity and Seebeck coefficient, which is an effective way to enhance the figure of merit ZT. SnCl4 doping can decompose into cation and anion which provide electrons and thus increase carrier concentration. The optimum carrier concentration was obviously increased to 1.17×1020cm−3. The electrical conductivity boosts from 0.05 to 5087 Sm−1 at 300 K. Coupled with the intrinsically suppressed thermal conductivity originating from weak chemical band and grain refinement, a higher ZT of 0.61 is obtained at 773 K for (Bi,Sb)1.95Sn0.05Se2.8Cl0.2, which is ten times higher than that of the un-doped BiSbSe3.