After the studying of remote image and wavelet decomposing coefficients, an improved algorithm is introduced based on SPIHT: The first-order low-frequency sub-band and high frequency sub-band are decomposed again and the four further decomposed sub-bands are coded respectively with different threshold; For the decomposed high-frequency sub-band, wavelet coefficients will not be coded and they will be given a fixed value when they are decoded. The improved algorithm deals with the wavelet coefficients in different sub-bands. The compression experiment of remote-image confirms the improved algorithm is effective.