Abstract: The vacuum residue that consists of SARA is usually considered as a stable colloid system. The changes of SARA of vacuum residue from Saudi and Iran light crude under different conditions in STRONG ebullated processing were investigated. The relations of the conversion and the stability of the systems during processing were analyzed by Spot test, Separability Number test and Colloid Stability Index test. The results indicate that Spot test can directly reflect the trend of the stability of the system. The inner spot begins to emerge in spot imaging figure when the conversion reaches to 43%, indicating the system turns into unstable. Colloid Stability Index (CSI) can quantitatively predict the stability variation.The system becomes unstable if CSI is smaller than 0.7, in accord well with the Spot test results; Based on the ability to resist dilution of the overall system, Separability Number has more accurate results than the other two methods, and when the Separability Number is larger than 33, the system becomes unstable obviously.