A fiber link detection method, wherein the method is applied to an optical communications network, the optical communications network comprises a first network device and a second network device, a first interface of the first network device communicates with a second interface of the second network device over a first fiber link, and the method comprises: obtaining, by the first network device, a forward delay value, wherein the forward delay value is used to indicate a forward delay of transmitting a precision time protocol, PTP, packet by the second interface to the first interface over the first fiber link; obtaining (S 102), by the first network device, a reverse delay value, wherein the reverse delay value is used to indicate a reverse delay of transmitting a PTP packet by the first interface to the second interface over the first fiber link; determining, by the first network device based on the forward delay value, the reverse delay value, and a first threshold, that the first fiber link comprises a third network device, wherein the first network device and the second network device support PTP, and the third network device does not support PTP; and wherein the determining (S 103), by the first network device based on the forward delay value, the reverse delay value, and a first threshold, that the first fiber link comprises a third network device comprises: calculating, by the first network device, a delay parameter of the first fiber link based on N forward delay values and N reverse delay values that are obtained within a preset time period; and determining, by the first network device based on the delay parameter and the first threshold, that the first fiber link comprises the third network device. obtaining, by the first network device, a forward delay value, wherein the forward delay value is used to indicate a forward delay of transmitting a precision time protocol, PTP, packet by the second interface to the first interface over the first fiber link; obtaining (S 102), by the first network device, a reverse delay value, wherein the reverse delay value is used to indicate a reverse delay of transmitting a PTP packet by the first interface to the second interface over the first fiber link; determining, by the first network device based on the forward delay value, the reverse delay value, and a first threshold, that the first fiber link comprises a third network device, wherein the first network device and the second network device support PTP, and the third network device does not support PTP; and wherein the determining (S 103), by the first network device based on the forward delay value, the reverse delay value, and a first threshold, that the first fiber link comprises a third network device comprises: calculating, by the first network device, a delay parameter of the first fiber link based on N forward delay values and N reverse delay values that are obtained within a preset time period; and determining, by the first network device based on the delay parameter and the first threshold, that the first fiber link comprises the third network device. calculating, by the first network device, a delay parameter of the first fiber link based on N forward delay values and N reverse delay values that are obtained within a preset time period; and determining, by the first network device based on the delay parameter and the first threshold, that the first fiber link comprises the third network device.