The basic theory of modal analysis is discussed briefly

the finite element model of fan blade is established.Through calculation and analysis

nature frequency and modal shape is found

and the vibration condition is analyzed in various order vibration model.Considering the influence of pre-stress for working blade

the nature frequency is calculated through loading revolving torque.Through comparing the nature frequency obtained from the finite element analysis and the exciting frequency by calculated under different speeds

the resonance of blade is analyzed.