The LUMO and HOMO energy levels (E-LUMO/E-HOMO) are key parameters for conjugated polymers, which can greatly affect their applications in organic optoelectronic devices. In this manuscript, with donor acceptor (D-A) type conjugated polymers based on double B-N bridged bipyridine (BNBP) unit, we report fine-tuning of komo of conjugated polymers in a wide range via substitutions on both D unit and A unit. We synthesize eight D-A type conjugated polymers with alternating electron-deficient BNBP unit and electron-rich bithiophene (BT) unit in the main chain. By changing the substitutes on BNBP or BT, the E-LUMO of these polymers can be finely tuned in a wide range from -3.3 eV to -3.7 eV. We comprehensively investigate the electronic structures, photophysical properties, charge-transporting properties and polymer solar cell (PSC) device applications of these polymers. In PSC devices, these BNBP-based polymers can be used either as electron donors (with high-lying kumo/EHomo) or as electron acceptors (with low-lying E-LUMO/E-HOMO). The PSC device with the BNBP-based polymer donor exhibits a PCE of 2.92% and the PSC device with the BNBP-based polymer acceptor exhibits a PCE of 5.16%. These results indicate a new approach to modulate the LUMO energy levels of D-A type conjugated polymers by modifications on both D unit and A unit.