Abstract: A method of dynamic thermal fouling was created to evaluate the stability of blended heavy oil. Using Lanzhou Vacuum Residue as stock, the evaluation conditions were discussed. Under the conditions of flow rate of 10 g/min, reactor wall temperature of 390 ℃ and sampling at 30 h, the reliable evaluation results can be obtained. The method was then used to examine the stabilities of Lanzhou Vacuum Residue (LZVR) with Lanzhou Ethylene Tar (LZET) blending system. The evaluation results that the fouling resistance and the temperature drop in reactor center from the wall increase with the increment of the ratio of LZET/LZVR indicate the decrease of stability of blending system. The results of the method are consistent with the analysis of mass fraction normalized conductivity. This demonstrate that dynamic thermal fouling method can track the phase separation and fouling of blended heavy oil dynamically, which provides supports for industrial blending process.