In view of the difficulty of testing the mechanical properties of smooth surface, a measuring system based on improved digital laser speckle interferometry is established. First, speckle illumination is achieved by designing a new speckle interferometer optical path. At the same time, the dynamic speckle interferograms of the smooth parts are processed using the spatial-carrier Fourier transform method. Finally, the distribution of the deformation field of the smooth surface is obtained. This method does not perform any processing on the surface to be measured, which enables high-precision full-field deformation measurement on a smooth surface. The experimental results show that the maximum deformation is at the center of the mirror plate and the maximum deformation is 1.936, 1.861 and 1.797 μm, respectively, which is close to the preset value of center deformation. The method has simple optical path, a practical measurement scheme, which can realize fast dynamic measurement of smooth surface deformation.