Droplet image feedback control system is designed for monitoring the evaporation effect at vapor-liquid interface in the space experiment on "SJ-10" recoverable satellite.Based on DSP,the system has three main functions:The first,to capture and store droplet images during the experiment; The second,to calculate droplet geometrical and physical parameters such as volume,surface area,surface tension,evaporation rate and contact angle at a high-precision level; The third,to keep the droplet volume constant.To realize these functions,the system captures images through CCD camera and output them to DSP at first,then they are compressed in DSP and be output to the host computer.The image preprocessing technology and connected component labeling algorism are used to extract the contour of droplet.