Abstract: Steam soak of horizontal wells is becoming a very im- portant and economical method in the thermal recovery of heavy oil reservoirs.The success of a cyclic steam injection project depends strongly on the selection of key parametcrs. To get better effect of steam soak,the key parameters of cy- clic steam injection have to be optimized and controlled. Based on the XingⅠformation,Shu-1 Du84 block,Liaohe oilfield heavy oil exploitable condition,the production histo- ry was matched.By optimizing the key parameters,such as cycle length,amount of steam injected,length of horizontal segment,steam injection pressure,steaming velocity,dry- ness fraction,the applicable plan was provided.Based on the optimized plan,we predicted performance of cyclic seam stimulation,such as cumulated oil.