A DSP based system is proposed to detect infrared small targets in thermal imaging. The core of the system is TMS320DM6467T, in which an ARM9 and a C64+ DSP are integrated. The system includes a video capture module, a video process module and a video output module. To detect small targets in the video, an algorithm based on maximum between-class variance method in wavelet domain is proposed. Video stream data is obtained by a thermal imager, and then processed in proposed system. Experiment shows that the system is capable of target detection for thermal imaging.