The invention discloses a speckle generating device and a speckle generating method with an adjustable contrast value. The speckle generating device comprises a continuous wave laser, wherein a light beam zoom unit, a polarizer, a diaphragm, a spatial light modulator, an analyzer, a Fourier lens and a CCD (Charge Coupled Device) camera are sequentially arranged in the forward direction of a light beam of the continuous wave laser; speckle field information generated by the spatial light modulator is imaged by the CCD camera and then is stored in a computer; the spatial light modulator and the CCD camera are connected with the computer respectively; an image on the spatial light modulator is written by the computer; the light beam zoom unit is used for controlling the beam waist size of a laser beam emitted to the spatial light modulator; the spatial light modulator is positioned on a front focal plane of the Fourier lens; the CCD camera is positioned on a rear focal plane of the Fourier lens. Moreover, the speckle generating device has the advantages of simple principle, simple device, online adjustment and the like and can be widely applied to the fields of laser speckle illumination microscopy technologies, speckle contrast value testing technologies and the like.