In down-looking synthetic aperture imaging ladar (SAIL), spatial parabolic wave-front phase differences are requested for two coaxial reverse scanned polarization-orthogonal beams at the rear focal plane of inner optical fields of the transmitter. Using self-heterodyne detection and phase complex-value processing, this kind of SAIL generates a linear phase modulation proportional to the lateral distance in the orthogonal direction, and a parabolic phase history concerted in longitudinal position of the target point in the travel direction, based on the imaging principles of Fourier transformation focus and two-order phase matched filtering, respectively. The novel rotatable structure with double-face reflectors is proposed, in order to make two coaxial polarization-orthogonal beams scan far field target with different directions and the same angular rate in the orthogonal direction. And then, cylinder lens is employed in one of polarization branches to control phase change of the travel direction beam. According to the theory of Fourier optics and mathematical approximation, the effect of the positions of double-face rotatable reflectors on the distribution of inner optical field is studied by theoretical analysis and formula derivation. Under physical model constructed, the diffraction of two coaxial polarization-orthogonal beams from laser to inner optical fields is simulated numerically. The comparison results of amplitude and wave-front phase distribution between the discrete simulation and formula analysis are given, and finally, error analysis and conclusions are obtained.