Bismuth oleate(BO) was synthesized from acetic anhydride, bismuth oxide and oleic acid by two - step reaction, and it was added to polyvinyl chloride (PVC) as thermal stabilizer in order to improve its thermal stability. The structure of bismuth oleate was characterized by Fourier transform infrared spectroscopy (FITR), mass spectrum(MS) and the composition of bismuth oleate was determinated by elemental analysis(EA) and EDTA complexometric titrati. At the same time, the interaction mechanism of bismuth oleate improving the thermal stability of PVC was investigated by thermal aging oven test, Congo red test, conductivity test, thermogravimetric analysis (TGA) and rheological curve. The results showed that the time of the initial whiteness of PVC sheet with 2.6% bismuth oleate was 60 min, and the static stability time of Congo red was 39.5 min, so the thermal stability of PVC was improved obviously. The bismuth oleate could be used as a liquid thermal stabilizer. Moreover, from the analysis of the test of the bismuth oleate for HCl and complexing mechanism, we considered that the bismuth oleate could improve the thermal stability of PVC products mainly by the means of oleate ions substituting unstable chlorine atoms.