Embodiments of the present invention disclose a key exchange method and apparatus, which relate to the communications field, and can enable user equipments establishing a D2D link to share a set of keys, and further, information security can be achieved when a user equipment transmits service data or a signaling message through a Ud interface. A network device acquires a first key, and sends a message including the first key to a second user equipment, so that the second user equipment uses, when communicating with a first user equipment by using a D2D link, the first key to protect transmitted information. Embodiments of the present invention are applicable to an exchange process of keys for protecting data on a D2D link.