Abstract: The phosphorus modified pillared rectorite catalysts were prepared and the coking behavior of the catalyst during the cracking of a light gas oil was examined.It has been found that the acidity and cracking activity of the phosphorus modified catalysts are increased and the anticoking ability of the catalyst,which is modified by suitable phosphorus compound,can be improved remarkably.So it is considered that the coking reaction is related to the amount of acid sites and the coordinated action of Lewis/Brnsted acid sites.