An optical line terminal and a method for upgrading a primary device and a secondary device of the optical line terminal are provided. The secondary device receives a stepwise reset notification sent by the primary device; the secondary device resets a control chip according to the received stepwise reset notification, and sends a request message to the primary device after the control chip is reset, where the request message is used to request the primary device to deliver new configuration data; the secondary device obtains the new configuration data delivered by the primary device; and the secondary device restores data of the control chip by using the new configuration data delivered by the primary device. In the embodiments of the present disclosure, only the control chip of the secondary device needs to be reset and upgraded, and other hardware structures of the secondary device do not need to be reset.