The n-type polycrystalline Bi2O2Se1-xClx (0x0.04) samples were fabricated through solid-state reaction followed by spark plasma sintering. The carrier concentration was markedly increased to 1.38x10(20) cm(-3) by 1.5% Cl doping. The maximum electrical conductivity is 213.0 S/cm for x=0.015 at 823 K, which is much larger than 6.2 S/cm for pristine Bi2O2Se. Furthermore, the considerable enhancement of the electrical conductivity outweighs the moderate reduction of the Seebeck coefficient by Cl doping, thus contributing to a high power factor of 244.40 WK(-2)m(-1) at 823 K. Coupled with the intrinsically suppressed thermal conductivity originating from the low velocity of sound and Young's modulus, a ZT of 0.23 at 823 K for Bi2O2Se0.985Cl0.015 was achieved, which is almost threefold the value attained in pristine Bi2O2Se. It reveals that Se-site doping can be an effective strategy for improving the thermoelectric performance of the layered Bi2O2Se bulks.