A network-connection redundant method for devices with cascade networking capability, comprising: initializing a network with a plurality of network nodes with routing capability and one or more networking devices with cascade networking and routing capability, preferably industrial control machines used to control various terminal devices, wherein each network node at least has two network ports and one or more device ports, and the network nodes respectively belong to separate parts of two or more different types of local area networks, and each networking device at least has two network ports each connecting the network port of the adjacent networking device or the device port of one of the network nodes to form a linear type network connected between the different types of local area networks, and the networking device connects an external network via the network node; defining roles of ports for each device port of each network node according to network packets generated by each network node and each networking device, wherein the roles of ports are a plurality of forward ports and one or more blocked ports, and one of the two device ports respectively connected the two ends of the linear type network is defined as the blocked port; each network node periodically broadcasting to the respective different types of the local area networks; the forward ports forwarding the broadcasting to the one or more networking devices; each network node confirming receiving a connection-confirmation packet; determining whether any connection changes among the one or more networking devices and the interconnected network nodes according to a relative response packet; if the connection does not change, continuously broadcasting connection-confirmation packet; if the connection changes, including failure of connection, failure of device, and modification of connection, redefining the roles of ports for each device port, and redirecting the connections of the one or more networking devices for avoiding a failed portion of the connection, wherein the device port connected the linear type network and defined as the blocked port is redefined as the forward port; and accomplishing a redundant connection. initializing a network with a plurality of network nodes with routing capability and one or more networking devices with cascade networking and routing capability, preferably industrial control machines used to control various terminal devices, wherein each network node at least has two network ports and one or more device ports, and the network nodes respectively belong to separate parts of two or more different types of local area networks, and each networking device at least has two network ports each connecting the network port of the adjacent networking device or the device port of one of the network nodes to form a linear type network connected between the different types of local area networks, and the networking device connects an external network via the network node; defining roles of ports for each device port of each network node according to network packets generated by each network node and each networking device, wherein the roles of ports are a plurality of forward ports and one or more blocked ports, and one of the two device ports respectively connected the two ends of the linear type network is defined as the blocked port; each network node periodically broadcasting to the respective different types of the local area networks; the forward ports forwarding the broadcasting to the one or more networking devices; each network node confirming receiving a connection-confirmation packet; determining whether any connection changes among the one or more networking devices and the interconnected network nodes according to a relative response packet; if the connection does not change, continuously broadcasting connection-confirmation packet; if the connection changes, including failure of connection, failure of device, and modification of connection, redefining the roles of ports for each device port, and redirecting the connections of the one or more networking devices for avoiding a failed portion of the connection, wherein the device port connected the linear type network and defined as the blocked port is redefined as the forward port; and accomplishing a redundant connection.