The invention discloses a computer network security control device. The computer network security control device comprises a first hard disk, a second hard disk, a network card, a plug-in connector, achange-over switch and a single-chip microcomputer. The first hard disk, the second hard disk and the network card are connected with the plug-in connector; the change-over switch is connected with single-chip microcomputer; a microprocessor, a fan and a fan controller are further included. A shielding device is arranged between the first hard disk and the second hard disk; the plug-in connectoris connected with the change-over switch through a relay; an electromagnetic sensor is arranged on the relay; the electromagnetic sensor is connected with the input end of the microprocessor; the output end of the microprocessor is connected with a network card through an isolator, a temperature sensor and a humidity sensor are arranged on the single-chip microcomputer, the temperature sensor andthe humidity sensor are connected with the input end of a fan controller, the output end of the fan controller is connected with a fan, and the fan is arranged below the single-chip microcomputer. Thechange-over is safe to use, good in heat dissipation effect and long in service life.