PtSnK/ZSM-5 catalysts with different amounts of K were prepared by the sequential impregnation method on HZSM-5 zeolites, and their catalytic activities and stabilities in propane dehydrogenation were investigated. The effect of the addition of K on the physicochemical properties was studied by means of BET, XRD, SEM, NH3-TPD, TPR, and TPO. The results indicated that the addition of K had an obvious impact on the catalytic performance of the PtSn/ZSM-5 catalyst. A suitable amount of K could not only change the acid of the catalysts but also improve the relation between metals and the support, thus reduce the deactivation rate and increase the selectivity to propylene. It was found that the propylene selectivity and yield could reach the maximum when the content of K was 0.8%.