A power-rail ESD clamp circuit with a silicon controlled rectifier and a control module is provided. The silicon controlled rectifier is connected to a high voltage level and a low voltage level for bearing a current flow. The control module is connected to the silicon controlled rectifier in parallel, and includes a PMOS, a NMOS, at least one output diode, a resistor and a conducting string. The silicon controlled rectifier is a P+ or N+ triggered silicon controlled rectifier. By employing the novel power-rail ESD clamp circuit, it is extraordinarily advantageous of reducing both a standby leakage current and layout area while implementation.