In order to study dynamic characteristic of spray boom, a parametric finite element model of spray boom was built in ANSYS, and the model was validated by experimental modal analysis. According to the result of spray boom modal analysis, the structure of the spray boom was optimized in ANSYS, in the condition of increasing the spray boom mass for 8.4%, increasing the first mode frequency from 9.16Hz to 10.41Hz, and avoiding from the resonance vibration section. Then, the deformation of the spray boom in operating before and after optimization was compared and analyzed in ADAMS. The result showed that the max horizontal deformation at the spray boom end before optimization Dbmax was 39.6mm, and the root-mean-square was 12.6mm. The max horizontal deformation at the spray boom end after optimization Damax was 10.1mm, and the root-mean-square was 2.9mm. The horizontal deformation was reduced.