A method of successive approximation to correct the horizontal and vertical divergences of the diffuse X-ray scattering was developed. The elastic constants of zinc calculated from the corrected thermal diffuse scattering intensity are (in dyne/cm2):c11=1.69,c12=0.394,c13=0.549,c33=0.682,c44=0.429,c66=(1/2c11-1/2c12=0.648. They are found to be in good agreement with those obtained from supersonic measurements.