Divergent angle of laser beam which used in laser guidance and measurement is an important parameter. Large area illumination of laser is also an important application in large-scale speckle interferometry. The relation between speckle size and elliptical Gaussian laser beam illumination parameter is derived by using speckle auto-correlation, and the effective two-dimensional lighting size at receiving plane is calculated, the divergence according to the lighting sizes at different distances futhermore determined. This device is simply constructed. Using laser speckle auto-correlation metrology methods the dynamic range of laser intensity is enlarged, ignoring the off-axis influence, and environmental light is suppressed.