Based on the theory of petroleum disperse system, three kinds of additives with good capability to keep the feedstock active were selected through the viscosity changes of raw materials. The results of experiment indicate that the additive can change the dispersion degree of the petroleum disperse system. When adding the no. 3 additive 0.1%, the solidifying point, refractive index and conductivity of the sample are the minimum, that is, the system is just in the optimum active state. The effect of three kinds of additives to catalytic cracking of the samples of Daqing crude mixes with 26% residue using fluid fixed bed. When temperature is 500 ℃, feedstock is 13.5~14.5 g, catalyst/oil ratio is 6, LHSV is 20 h-1, the yield of dry gas decreases by 2.5%~3.0%, coke yields decrease by 1.5%~2.5%, LPG yield increases by 2.5%~3.5%, gasoline yield increases by 2.5% ~ 3.5%, and the yield of diesel decreases slightly.