A technique is investigated which uses a laser to measure two components of the transverse velocity of diffuser.On the basis of the derivation of space-time correlation function on the far-field dynamic speckle, a computer-aided detection system is presented. The correlation properties are approached by using the system. The relationship between vector components of the transverse velocity of a diffuser and differentially spatial-temporalcorrelation function of dynamic speckle is shown to be linear. Hence it is possible to measure the velocity vector of a moving diffuser by evaluating the space-time correlation of dynamic speckle. The experimental results are presented to illustrate the theory.