A delay measurement method, applied to a master terminal, comprising: determining at the master terminal a first information frame according to a first timestamp value obtained in advance; transmitting by the master terminal a first preset overhead byte carrying the first information frame to a slave terminal, wherein the first information frame carries the first timestamp value, and the first preset overhead byte is an overhead byte in a Synchronous Digital Hierarchy, SDH, protocol; receiving at the master terminal a second preset overhead byte carrying a second information frame fed back from the slave terminal, wherein the second preset overhead byte is an overhead byte in the SDH protocol; and determining at the master terminal a data transmission delay according to the first timestamp value, a second timestamp value and a third timestamp value carried in the second information frame and a fourth timestamp value obtained in advance; wherein, the first timestamp value, the second timestamp value, the third timestamp value and the fourth timestamp value are determined by: obtaining at the master terminal a current timestamp value of a local clock of the master terminal, and taking the current timestamp value as the first timestamp value corresponding to the first information frame, in response to receiving a master mode start instruction and monitoring the arrival of the first preset overhead byte in a data stream; in response to receiving at the slave terminal the first preset overhead byte carrying the first information frame, obtaining at the slave terminal a current timestamp value of a local clock of the slave terminal, and taking the current timestamp value as the second timestamp value; determining at the slave terminal the third timestamp value as the moment when a preamble in the second information frame is interpolated into the second preset overhead byte by the slave terminal; and obtaining at the master terminal a current timestamp value of another local clock of the master terminal, and taking the current timestamp value as the fourth timestamp value, in response to receiving the preamble in the second information frame. determining at the master terminal a first information frame according to a first timestamp value obtained in advance; transmitting by the master terminal a first preset overhead byte carrying the first information frame to a slave terminal, wherein the first information frame carries the first timestamp value, and the first preset overhead byte is an overhead byte in a Synchronous Digital Hierarchy, SDH, protocol; receiving at the master terminal a second preset overhead byte carrying a second information frame fed back from the slave terminal, wherein the second preset overhead byte is an overhead byte in the SDH protocol; and determining at the master terminal a data transmission delay according to the first timestamp value, a second timestamp value and a third timestamp value carried in the second information frame and a fourth timestamp value obtained in advance; wherein, the first timestamp value, the second timestamp value, the third timestamp value and the fourth timestamp value are determined by: obtaining at the master terminal a current timestamp value of a local clock of the master terminal, and taking the current timestamp value as the first timestamp value corresponding to the first information frame, in response to receiving a master mode start instruction and monitoring the arrival of the first preset overhead byte in a data stream; in response to receiving at the slave terminal the first preset overhead byte carrying the first information frame, obtaining at the slave terminal a current timestamp value of a local clock of the slave terminal, and taking the current timestamp value as the second timestamp value; determining at the slave terminal the third timestamp value as the moment when a preamble in the second information frame is interpolated into the second preset overhead byte by the slave terminal; and obtaining at the master terminal a current timestamp value of another local clock of the master terminal, and taking the current timestamp value as the fourth timestamp value, in response to receiving the preamble in the second information frame. obtaining at the master terminal a current timestamp value of a local clock of the master terminal, and taking the current timestamp value as the first timestamp value corresponding to the first information frame, in response to receiving a master mode start instruction and monitoring the arrival of the first preset overhead byte in a data stream; in response to receiving at the slave terminal the first preset overhead byte carrying the first information frame, obtaining at the slave terminal a current timestamp value of a local clock of the slave terminal, and taking the current timestamp value as the second timestamp value; determining at the slave terminal the third timestamp value as the moment when a preamble in the second information frame is interpolated into the second preset overhead byte by the slave terminal; and obtaining at the master terminal a current timestamp value of another local clock of the master terminal, and taking the current timestamp value as the fourth timestamp value, in response to receiving the preamble in the second information frame.