In this paper,we formulate a SIVS epidemic model with special recovery rate to study the impact of limited medical resource on the transmission dynamics of diseases with vaccination.The basic investigation of the model has been finished. The backward bifurcation has been proved precisely. It is shown that limited medical resource leads to vital dynamics,such as bistability. Backward bifurcation implies that even if the basic reproduction number is smaller than unity,there may be a stable endemic equilibrium and the basic reproductive number itself is not enough to describe whether a disease will prevail or not and we should pay more attention to the initial conditions. It is also shown that suffi-cient medical services and medicines are very important for the disease control and eradication. Besides,the impact of vaccination has been explored too.