The coherent scattering of Gaussian beam by arbitrarily shaped convex dielectric object with rough surface is investigated. Based on the plane wave spectrum method, the scattered field of Gaussian beam from rough object is derived and the formula for calculating the coherent scattering cross section is obtained using the physical optics approximation and the stationary phase method. Compared with the result of plane wave, additional beam factor represents the effect of Gaussian beam, which is related to beam waist size, distance from beam waist to object center and the illuminated area on object, together with the incident or scattering angles. Finally the 1.06 μm laser beam scattering from rough sphere is numerically computed, and the influence of the beam factor, permittivity and polarization on coherent LRCS is analyzed. It is shown that the results of Gaussian beam will approach that of plane wave when the beam radius is much larger than the size of object.