The invention provides conversion device and method from a CAN network to an ethernet network, which satisfy the safety level demands, for a digital safety monitoring device of a nuclear power station fast reactor process monitoring system. The device is structurally characterized by comprising a CAN transceiver, a singlechip, an ethernet network transceiver and a power supply, wherein a CAN controller is integrated in the singlechip, and a work pattern control switch is connected between the CAN transceiver and the singlechip. The controller of the singlechip is initialized when an operatingdevice is started, and then carries out the master control flow comprising the following steps of: a. sending ethernet network data and CAN data; b. receiving the CAN data; c. handling timer overflow; and d. sending the ethernet network data. An additionally arranged hardware switching switch effectively controls that the data is not allowed to be sent to the CAN network under the monitor mode. In the method, the network state monitoring function and the automated initialization function are provided for the device.