A new SIS model based on reinfection in complex networks was proposed.By using the model in the network with a treelike sturcture,not only the infection of descendants of an infected node was considered but also the reinfection of ancestor by the infected node was taken into account.Through theoretical analysis and numerical simulation on smallworld networks and scalefree networks,it is found that:for smallworld networks,the stationary infected density on this new model is larger than that on the traditional SIS model,and the shorter the infection time is,the gerater the stationary infected density will be;however for the scalefree networks,the stationary infected density on this new model is still larger than that on the traditional SIS model,yet the effect of the infection time on the stationary infected density can be neglected .