The invention discloses a silicon controlled rectifier used for ESD protection. The silicon controlled rectifier includes a pull-up silicon controlled rectifier, a pull-down silicon controlled rectifier, an isolation resistor, a NMOS transistor and a PMOS transistor. The pull-up silicon controlled rectifier comprises a first N well, which consists of a first P+ implanted region and a first N+ implanted region, and a first P well, which consists of a second P+ implanted region and a second N+ implanted region. The pull-down silicon controlled rectifier comprises a second N well, which consists of a third P+ implanted region and a third N+ implanted region, and a second P well, which consists of a fourth P+ implanted region and a fourth N+ implanted region. In the invention, a voltage clamp structure is formed through a PN diode structure and a well resistance structure which are parasitic on the silicon controlled rectifier; fast response of an ESD pulse and preopening of a protective structure can be achieved. By using the invention, opening speed is fast, weak gate oxide layer can be protected from instant and quick ESD static shock.