According to the feature of imaging spectrometer, compression of a two-dimension Image is converted into a series of one dimension processings. A real-time "two-true-value linear prediction method" has been developed to have the ability of on-board compressing the original data in the spectrum direction. This method can preserve absorption peak information during compression/decompression process. The results show that for most spectra at least 2:1 compression ratio has been obtained under 1% reconstruction accuracy, on an average the original data rate can be reduced by 3~4 limes. The art for coding compressing data, and the decom ression error has also been described.