Lasers with high stability of frequency are required on ultra-cold atom experiment. A compact frequency stabilization system of diode laser is proposed,which is based on the principle of saturated absorption of atom vapor. The generation,amplification,filtering,mixing of radio frequency (RF) modulation signal,as well as the error signal detection,are integrated into a 3U plug-in module. The scan circuit for finding the spectroscopy and PI controller for frequency locking are also integrated into another 3U plug-in module. For holding those modules,a 3U rack of 14-slot and 19 inches (482.6 mm) width is designed. Experiments show that the high level of integration means not only take up less space,easy to manage and maintain,but its anti-interference ability also greatly enhanced. In order to detect the faster phase jitter of the laser diode,and to avoid the noisy low frequency,a modulation frequency as high as 21.4 MHz is adopted.