A method for determining a sending period of a packet in a deterministic network and an apparatus are disclosed. The method includes: receiving a first packet; determining a first period, where the first period is a sending period of the first packet; determining timestamp information of the first packet based on the first period, where the timestamp information is used to indicate a time difference between a first time and a second time, the first time is a time at which the first packet starts to be sent in the first period, and the second time is a start time of the first period; encapsulating the timestamp information into the first packet to obtain a second packet; and sending the second packet.