We present a cluster immunization strategy and study its immune effect on scale-free network with tunable clustering in a modified classic rumor propagation model. Study shows that effect of cluster immunization becomes better with increasing of network clustering coefficient. Several immunization strategies including target immunization, betweenness immunization, closeness immunization and cluster immunization are compared. It shows that betweenness immunization is always the best regardless of network clustering. As a network clustering coefficient is relatively great,effect of cluster immunization is better than that of closeness immunization and close to target immunization. With further increasing network clustering coefficient,cluster immunization exceeds target immunization and approaches to betweenness immunization.