A coded aperture spectral imaging system uses a spatial light modulator to encode target information. It subsequently maps the signal onto a two-dimensional detector array and forms spatial and spectral aliasing information. Further, a spectral data cube can be reconstructed using a suitable reconstruction algorithm. In this study, we propose a multi-slot combination coding method, which is encoded in only one direction, to improve the coding efficiency. This procedure is selected because dispersion occurs in only one direction. When compared with the two-dimensional random coding method that is currently being applied, this approach simplifies the mathematical model and its analysis while reducing the coding complexity,under the premise of obtaining identical reconstruction results. Further, the switching characteristics of the liquid crystal light valve are used in the coding. The spectral imaging system is assembled by incorporating a PGP (prism-transmission grating-prism) beam-splitting component. Different sampling rate experiments are conducted, and highly accurate recovery results are obtained. The feasibility of the proposed coding method can result in innovation in the future coded spectral imaging systems.