In the space solar telescope(SST)mission,because of the conflict of large volume of observation data and limited resources for store and transmission,the onboard data compression is needed.According to the requrements of data processing and the ability of native development,we adopt an in-line compression scheme.In this paper,the algorithm based on the wavelet transform is given and optimized on the hardware platform using DSP and FPCA.Data compression unit(DCU)can compress the solar images into 1/5 of original data and the processing time is less than 6 seconds,and the SNR is greater than 26 dB which satisfies the SST images requrements.DCU realizes the implement of native SDPU,which has passed the examination.