Abstract: This paper presents the influence of the modified matrices of RFCC catalysts on the acidity and activity. The result shows that the surface area, pore volume and acidity of kaolin clay are all increased when it is baked and modified with acid. It also shows that when aluminum oxide is modified with phosphorus, its acid site is increased but acid strength is weakened. When these modified materials are used as the matrices of the olefin-reduce residual oil cracking catalysts, the activity for cracking and hydrogen-transfer as well as isomerization raise and the coke yield reduces.