On the basis of down-looking synthetic aperture ladar (DL-SAL), a kind of self-interferometric SAL for 3D topographic relief imaging is proposed in this paper. Firstly, the forward-scanning and backward-scanning cylinder lenses for imaging along the orthogonal direction of travel are biased in their positions, it thus introduces a shifted spectrum image with a linear phase term. Then pair of a forward-scanning resulted focused image and the next backward-scanning resulted image are coherently added, therefore a self-interference between the two images occurs. The flat fringes from this self-interference can be obliquely projected to a target plane, so that a subtly rippled interferogram containing the target height information can be observed. Finally, by using the unwrapping algorithm, a contour mapping representing the surface profile will be achieved. This SAL including a transmitter and a receiver realites the 3D imaging by a one-pass interferometry. The features are simple in construction and effective in principle. Moreover, the phase errors from the atmospheric turbulence can be automatically compensated.