The sieve box is the major working part in fluidized bed, which bears the repeating dynamic loading. It generally works in severe condition, and the strength is a problem. In this paper, the vibration of the sieve box was analyzed with finite elemental method. Firstly, a 3D model of the box was constructed by PRO/E. Then the modal analysis and harmonic response of the model were investigated using ANSYS WORKBENCH. Based on the modal analysis theory，some parts of the sieve box were structurally optimized to avoid resonance. The simulation procedure adopted in the study and the achieved results could definitely facility the fluidized bed design and improve the design efficiency.