The characteristics of laser scattering of rough surfaces composed of periodical and random components generated by mechanical machining were researched. Based on the Helmholtz-Kirchhoff integration theorem and some statistic theories, the formula for calculating the scattering field distribution in the space of rough surfaces was derived. According to the derived formula, the scattering coefficients of rough surfaces with different amplitudes of the periodic component and different roughnesses of the random component were obtained. Meanwhile, the spatial distribution characteristics of the scattering field and its formation were analyzed. The experiments show when the roughness of random component is far less than the laser wavelength, the number of the diffraction fringes augment with the increase of the amplitude of the periodic component. While the roughness of random component is comparable with the magnitude of the laser wavelength, the amplitude of the periodic component has a little effect on the scattering field distribution within the range of laser wavelength and the diffraction fringes are disappear. In this circumstance, the scattering field distribution in the space is considered to be modulated by changing the amplitude of the periodic component.