Abstract: The rapid development of microblogging not only has led people into the We-Media era, but also creates favorable conditions for the rapid dissemination of information. Taking direct immunization into consideration, an improved SIR model was presented which uses differential equations to study the rules of information dissemination and to predict information on microblogs. The experiment result shows that the improved SIR model can effectively reflect the rules of information dissemination, and can predict microblog information dissemination more precisely than the microblog standard SIR model.