This application relates to a slot negotiation method and a device. The method includes: A transmitter sends a first FlexE overhead frame to a receiver, to request active/standby calendar switching. When the receiver is in a restart state, the receiver does not respond to the received first FlexE overhead frame. In addition, the RX sends a routine update second FlexE overhead frame to the transmitter. Determining that the second FlexE overhead frame is not a response to the first FlexE overhead frame, the transmitter sends a third FlexE overhead frame to request active/standby calendar switching again. According to the method in this application, incorrect calendar switching on the transmitter side caused by a mistaken response of the receiver can be avoided. This reduces the likelihood of a service interruption caused by the existing slot negotiation mechanism.