The spaceborne synthetic aperture radar (SAR) sparse flight 3-D imaging technology through multiple observa-tions of the cross-track direction is designed to form the cross-track equivalent aperture, and achieve the third dimensionality recognition. In this paper, combined with the actual triple star or-bits, a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal com-ponent analysis (PCA) is presented. Firstly, interferometric pro-cessing is utilized to reach an effective sparse representation of radar images in the frequency domain. Secondly, as a method with simple principle and fast calculation, the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics. Finally, the 3-D image can be ob-tained by inverse transformation of the reconstructed spectrum by the PCA. The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-fre-quency sidelobe noise introduced by sparse flight with a sparsity of 49％ and random noise introduced by the receiver. Mean-while, due to the influence of orbit distribution of the actual triple star orbits, the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and refer-ence to illuminate the significance of orbit distribution for this re-construction results. This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.