Starting from the Helmholtz Equation, the integral equation of light wave on medium interfaces is obtained by use of Green theorem. Then the integral equation is discretized into a set of linear equations with unknown values of light wave and its derivative on the interface. Numerical solutions of these linear equations give the values of light waves. This method is applied to the calculations of both the pinhole diffraction in subwavelength scale and random light field produced by random self-affine fractal surfaces in near field. A method for generation of random self-affine fractal surfaces is proposed by analogy to the derivation process of the autocorrelation functions of speckles in Frauhofer plane, and the Fourier transformation method for numerical derivative of the random surfaces is presented. The calculated results show that in near field, the random light fields vary dramatically with the distance increasing from the random surfaces, and the properties of light wave propagation are quite different from those of the light waves in far field.