The invention provides a monitoring system and a monitoring relay device. The monitoring relay device comprises a first type signal transceiver module, a second type signal transceiver module, a communication module and a control module, wherein the control module is electrically connected to the first type signal transceiver module, the second type signal transceiver module and the communicationmodule; the first type signal transceiver module is configured to obtain a first monitoring signal according to a first communication protocol that is associated with the communication protocol of a low-power wide-area network; the second type signal transceiver module is configured to obtain a second monitoring signal according to a second communication protocol; the communication module is configured to transmit a signal via a mobile network or a fixed communication network; and the control module is configured to instruct the communication module to selectively provide the first monitoringsignal or the second monitoring signal to a server via the mobile network or the fixed communication network. The invention overcomes the problem that the efficiency of the previous monitoring systemneeds to be improved by providing a monitoring system and a monitoring relay device that support a transmission protocol associated with the low-power wide-area network.