A series of anion exchange membranes (xPip-30%18PBP) containing both long hydrophobic (with an octadecyl grafting degree of 30%) and flexible hydrophilic (with an alkyl piperidine grafting degree of x) side chains were prepared by introducing octadecyl side chains and flexible hexyl piperidine cationic side chains synthesized with the main raw materials of 1-(6-bromohexyl)-1-methylpiperidine ionic salt (Br-6-Pip) and 1-bromooctadecane into the molecular structure of poly(biphenylpyridine) polymer through Menshutkin reaction. Their chemical structure was characterized by 1HNMR, and the microstructure was observed using SEM and TEM. The effects of the alkyl piperidine grafting degree on the performance of the xPip-30%18PBP membrane were investigated through various tests, including physical property measurements, TGA, mechanical properties, ion conductivity, vanadium ion permeability, and vanadium redox flow battery performance. The results indicate that the xPip-30%18PBP membrane exhibits a well-defined microphase separation structure. As the grafting degree of the flexible alkyl piperidine side chains increases from 40% to 70%, the significance of the microphase separation structure within the membrane also progressively enhances. With the increase in flexible piperidine grafting degree (from 40% to 70%), the ion exchange capacity of the xPip-30%18PBP membrane increases from 2.26 mmol/g to 2.88 mmol/g, the water uptake at 20 ℃ rises from 53.8% to 82.6%, and the swelling ratio increases from 9.9% to 23.4%. The ionic conductivity improves from 28.9 mS/cm to 41.9 mS/cm, while the membrane surface resistance decreases from 0.76 Ω·cm2 to 0.39 Ω·cm2. The tensile strength gradually decreases from 9.6 MPa to 5.7 MPa, while the elongation at break gradually increases from 19.8% to 35.5%. The vanadium ion permeability range from 1.32×10-6 cm2/min to 2.16×10-6 cm2/min. At a grafting degree of 60%, the 60%Pip-30%18PBP membrane demonstrates optimal comprehensive performance. A vanadium redox flow cell assembled with this membrane achieves an energy efficiency of up to 80.0% at a current density of 40 mA/cm2. After 200 charge-discharge cycles at a current density of 100 mA/cm2, the coulombic efficiency remains around 91% to 92%, while the energy efficiency decreases by only 4.2%.