A test system for overclocking capability of a central processing unit (CPU) includes a basic input and output system (BIOS), a frequency generator, and a watchdog timer. The BIOS includes an input module, a watchdog control module, and a frequency increasing module. The input module inputs an initial frequency of a CPU to the frequency generator to adjust a real-time frequency of the CPU. The watchdog control module sends a counter signal to the watchdog timer in a preset time interval. The watchdog timer receives the counter signal. If the watchdog timer does not receive the counter signal within the preset time, the watchdog timer outputs a reset signal to restart the computer. The frequency increasing module adds a preset increment to the real-time frequency to obtain a newly adjusted frequency, and provides the newly adjusted frequency to the frequency generator to adjust the real-time frequency.