A computer system for automatically overclocking includes an overclocking element, a detecting circuit and a basic input/output system (BIOS). The overclocking element has a signal standard. The detecting circuit is used for acquiring an I/O signal of the overclocking element. The BIOS is used for comparing the signal standard with the I/O signal to obtain a comparing result. The BIOS is further used for adjusting a reference signal according to the comparing result. The reference signal is an input signal of the overclocking element.