Ultra-narrow bandgap (ultra-NBG) small molecule acceptors (SMAs) show great potential in organic solar cells (OSCs) due to the extend-ed near-infrared (NIR) absorption. In this work, a synergetic alkoxy side-chain and chlorine-contained end group strategy is employed to achieve A-DA’D-A type ultra-NBG SMAs by introducing alkoxy chains with oxygen atom at the second position into the thiophene β posi-tion as well as replacing the F atoms with Cl atoms in the end group. As a result, the heptacyclic BZO-4F shows a redshifted absorption onset (960 nm) than Y11 (932 nm) without oxygen atoms in the side chains. Then, the fluorinated end groups are substituted with the chlorinated ones to synthesize BZO-4Cl. The absorption onset of BZO-4Cl is further redshifted to 990 nm, corresponding to an optical ultra-NBG of 1.25 eV. When blending with the polymer donor PBDB-T, the binary devices based on PBDB-T: BZO-4F and PBDB-T: BZO-4Cl delivers power conversion efficiencies (PCEs) over 12%. Furthermore, ternary devices with the addition of BZ4F-O-1 into PBDB-T: BZO-4Cl system achieve the optimal PCE of 15.51%. This work proposes a synergetic alkoxy side-chain and chlorine-contained end group strategy to achieve A-DA’D-A type ultra-NBG SMAs, which is important for future molecular design.