Abstract: In the material mechanics,the deflection of metal girder is a minute movement,and can't be measured using the normal regulation.This paper discusses the method of recurrence of the deflection of metal bar by means of holography,and calculates the deflection of metal bar according to the theory of deflection.The computing result is well in accordance with that of the laser holographic experiment,which proves that laser holography is a new intuitional and effective study method for metal material.