This paper dynamically discussed the development mechanisms of local rainstorm triggered by gravity waves，and proposed a feasible method，which was verified by a case study，to forecast the propagations of gravity waves． The results showed that:( 1) the propagation of gravity waves strictly consistent with the potential temperature ridge，and by analyzing the isentrope，the forecasting of the generation and evolution of gravity waves would be more effective; ( 2) the waves could travel from higher potential temperature to lower side，or propagate in reverse orientation; ( 3) there were corresponding relations between the propagation path of gravity waves and the surface convergence line． Though the waves propagated along with the convergence line，it did not generate the gravity waves;
( 4) in a case of rainstorm on 9th August 2011 in Shijiazhuang，the gust front generated the gravity waves as a triggering mechanism， and brought about strong rainfall in the west urban．