OBJECTIVE To study the vasorelaxant effects and mechanism of polyphenol compound 2，4′，5′-trihydroxy-5，2′- dibromo-diphenyl-methanone（LM49）on isolated aortic rings of rats. METHODS Thoracic aortic vascular rings of rats were collected. Using the diastolic rate as index ， the effects of different concentrations of LM 49 on endothelium-intact and endothelium-denuded aortic rings pre-contracted by norepinephrine （NE，1×10－6 mol/L）or KCl （60 mmol/L）were investigated. After pre-culturing vascular rings by nitric oxide synthase inhibitor L-nitro-arginine methyl ester （L-NAME，0.1 mmol/L） and cyclooxygenase inhibitor indomethacin （1×10－5 mol/L），as well as pre-culturing vascular rings by 4 potassium channel blockers [BaCl 2（0.1 mmol/L），tetraethylammonium（TEA，5 mmol/L），4-aminopyridine（4-AP，0.1 mmol/L）and glibenclamide （1×10－5 mol/L）]，the vasorelaxant effect of different concentrations of LM 49 on the vascular rings were investigated by using the same method. With the percentage of vasoconstriction as the index ，using KCl （60 mmol/L），NE（1×10－6 mol/L），calcium channel blocker verapamil （1×10－6 mol/L）and sarcoplasmic Δ 基金项目 重大新药创制国家科技重大专项 （No.2018ZX097- reticulum Ca 2 +-adenosine triphosphate （ATP） enzyme pump inhibitor thacarotene （TG，1×10－6 mol/L）to induce the release of calcium in vascular rings in the absence of calcium. CaCl was added cumulatively ，and the effect of LM 49 on the cxyw06，vasoconstriction caused by calcium influx induced by CaCl 2 was investigated. RESULTS 3×10－6，5×10－6，1×10－5 mol/L LM49 had a significant relaxation effect on NE and KCl precontracted vascular rings （P＜0.01）； whether the endothelium was removed or not had no significant effect on the vasodilation of LM 49（P＞0.05）. After L-NAME ，indomethacin， TEA and 4-AP was pre-incubated ，different concentrations of LM 49 had no significant effects on aortic rings precontracted by NE （P＞0.05）. Glibenclamide and BaCl 2 could inhibit the vasorelaxant effects of LM 49 on aortic rings precontracted by NE （P＜0.01）. In the absence of calcium ，LM49 could inhibit the contraction caused by calcium influx induced by accumulated CaCl 2 after pre-incubation with KCl ，NE，verapamil and TG （P＜0.01）. CONCLUSIONS LM49 evokes significant relaxation of isolated aortic vascular rings without endothelium dependence ；the mechanism of which is inducing ATP-sensitive potassium channel ， inward rectifier potassium channel open and restraining extracellular Ca 2 + influx via voltage-gated calcium channel ， receptor-operated calcium channel and store-operated calcium channel.