The invention discloses a control circuit, a connectivity controller, a connectivity control method and a main board, and belongs to the field of computers. The control circuit comprises the connectivity controller, a PCH, a BMC, a converter, a first storer and a second storer, wherein the first storer is used for storing an ME mirror image, and the second storer is used for storing a BIOS image. According to the control circuit, the ME mirror image and the BIOS image are stored in the first storer and the second storer respectively, and therefore in the process of upgrade of the BIOS, the BMC can upgrade the BIOS image stored in the second storer through a third SPI bus and a fourth SPI bus. The control circuit, the connectivity controller, the connectivity control method and the main board solve the problem that the SPI buses between the PCH and the SPI are disconnected in the process of upgrade of the BIOS, and achieve the purposes of guaranteeing normal operation of system services in the process of upgrade of the BIOS, and saving a large amount of software overhead.