Disclosed are a network security protection method, device and system. Said method includes: when a signal fault on a link of an optical transmission network is detected, determining, according to the signal fault, an optical transmission network interface where a failure has occurred (101); according to a service configuration path, transferring said signal fault to a packet transmission network interface corresponding to said optical transmission network interface (102); through said packet transmission network interface, transmitting a forward fault indication or an alarm indication signal to the packet transmission network in order to trigger said packet transmission network to perform an automatic protection switching (103); and / or, when a failure signal on a packet service channel of the packet transmission network is detected, determining, according to the failure signal on said packet service channel, a packet transmission network interface where a failure has occurred (104); according to the service configuration path, transferring said failure signal to an optical transmission network interface corresponding to said packet transmission network interface (105); through said optical transmission network interface, transmitting the signal fault to the optical transmission network in order to trigger said optical transmission network to perform a sub-network connection protection switching (106).