Embodiments of the present invention provide an MTC device authentication method, an MTC gateway, and a related device, which are used to solve a problem that direct interaction between a large quantity of MTC devices and a network side brings a heavy load to a network when the MTC devices are authenticated in the prior art. The method includes: performing, by an MTC gateway, mutual authentication with a core network node; performing, by the MTC gateway, mutual authentication with an MTC device; reporting, by the MTC gateway, a result of the mutual authentication with the MTC device to the core network node; and providing, by the MTC gateway, a non access stratum link protection key K between the MTC device and the core network node according to a key K1 or a key K2.