An automatic frequency stabilization system of external cavity diode laser based on digital signal processing (DSP) technology is achieved. The automatic frequency stabilization system uses saturated absorption spectroscopy of rubidium atom as the frequency reference and obtains error signal by modulation and demodulation technology. The system continuously collects saturated absorption signal and error signal by analog-to-digital converter at a fixed rate, the collected digital signal is treated and analyzed by DSP chip. The DSP chip controls the switch of modulation signal by its general purpose input output, and realizes the control of laser frequency scanning and digital feedback outputting by digital-to-analog converter. The laser frequency stabilization technology can not only stabilize the frequency of external cavity diode laser automatically, but also relock laser frequency in time after losing lock by evaluating the lock state of laser in real time, which improves the long-time running ability of the laser. Finally, the laser that uses the laser frequency stabilization technology is applied to a prototype of cold atomic clock in space, and it can meet the needs of relevant scientific experiments.