In the three-dimensional reconstruction of urban areas and man-made infrastructure, the urgent problem of SAR tomography is how to achieve satisfactory elevation resolution with a small number of non-uniform passes and preserve azimuth-range resolution simultaneously. An imaging method for SAR tomography based on RELAX algorithm is proposed in the framework of deterministic models. Compared with the spatial spectral estimation method that works statistically, this method does not need to deal with a spatial multilooking and maintains high resolution of direction dimension-distance dimension. Compared with the singular value decomposition method, this method has much better resolution of elevation dimension. Results obtained by processing simulated data and real data of ENVISAT-ASAR verified the promising potentiality of this imaging method.