Targeted inhibition of a drug efflux transporter P-glycoprotein (P-gp) is an important strategy to reverse multidrug resistance in cancer chemotherapy. In this study, a rationally structural simplification to natural tetrandrine was performed based on molecular dynamics simulation and fragment growth, leading to an easily prepared, novel, and simplified compound OY-101 with high reversal activity and low cytotoxicity. Its excellent synergistic anti-cancer effect with vincristine (VCR) against drug-resistant cells Eca109/VCR was confirmed by reversal activity assay, flow cytometry, plate clone formation assay, and drug synergism analysis (IC50 = 9.9 nM, RF = 690). Further mechanism study confirmed that the OY-101 was a specific and efficient P-gp inhibitor. Importantly, OY-101 increased VCR sensitization in vivo without obvious toxicity. Overall, our findings may provide an alternative strategy for the design of novel specific P-gp inhibitor as an anti-tumor chemotherapy sensitizer.