Bridge crane and gantry crane are the equipments which are the most widely used in lifting field,and it is necessary to study its dynamic characteristics when the gantry crane is designed. Taking the L type gantry crane as an example,with the help of finite element method,the crane’s top six order natural frequency and vibration mode were obtained by modal analysis,and the frequency biggest impacting on the dynamic characteristics of crane was obtained by harmonic response analysis,then taking the frequency as index,the dynamic sensitivity analysis of its structural parameters was carried out. In the dynamic sensitivity analysis,the parameters which affect dynamic characteristics of the crane structure more greatly were obtained. By the way,the dynamic optimization model can be simplified. The results provide the basis for the further optimization of the structure and the reference for the dynamic design of other similar structures.