The mathematical model of Fresnel hologram is analyzed,and it is found that the speed bottleneck of generating CGH is the operation of square and trigonometric function.A method for fast computation of Fresnel hologram is proposed.The mathematical model of Fresnel hologram is transformed to the form which is expressed as the four arithmetic operations of components related to horizontal direction and vertical direction of hologram,according to trigonometric identity.Then,the great amount of operation of square and trigonometric function is replaced by little amount of operation of square and trigonometric function and great amount of arithmetic operation.The computational amount of Fresnel hologram is reduced and the computational speed will be increased clearly.The experimental results show that the speed of Fresnel hologram computation is accelerated over 9 times by using the method of separation of variables.