A multi-band channel encrypting switch control device is provided. The device comprises a transmission part and a receiving part. The transmission part comprises: a first controller to store a secret key and to send a digital signal; an encrypting unit to encrypt the digital signal; a multi-band transmitter to select a plurality of wavebands to transmit the encrypted signal on the plurality of wavebands under control of the secret key; and a switch. The receiving part comprises: a multi-band detector to receive the encrypted signal transmitted on the plurality of wavebands; a decrypting unit to decrypt the encrypted signal; and a second controller to store the secret key and to decide whether or not to issue a switch signal by processing the signal and making decisions using the process result. A transmission device, a receiving device, and a control method are also provided. The encrypted data is transmitted via different channels to reduce possibility of signal interception during the transmission, thereby improving security significantly.