In the recent years the problem of electromagnetic interference (EMI) is increased to overcome this interference spread spectrum clock generator is used. As the operating frequency of electronic systems increases, the electromagnetic interference (EMI) effect becomes a serious problem in modern IC designs. Thus, the radiated emissions of system should be kept an acceptable level to ensure the function and performance of system and adjacent devices. Many approaches have been proposed to reduce EMI, such as shielding box, skew-rate control, and spread-spectrum clock generator (SSCG). Because SSCG modulates the system clock directly which is the major contributor of system EMI, it can lower the radiated emission significantly with less increase of extra cost and becomes the most popular solution among these techniques for SoC applications. Programmable all-digital spread spectrum clock generator (ADSSCG) suitable for System-On-Chip (SoC) applications with ultra-low-power capability is presented. Based on the timing constraint of system, the programmable ADSSCG can provide the suitable frequency spread ratio to obtain the optimal combination of timing deviation and EMI reduction for system applications. The proposed ADSSCG can provide an accurate programmable spreading ratio with process, voltage and temperature variations. To maintain the frequency stability of the system the triangular modulation and the fast relocked mechanism are used.