Submarine optical communication cables are the main infrastructure for modern international communication. Due to the presence of underwater bedforms， the difficulty to lay optical cables on the seabed is increased. If the amount of cable laid is less than required， it would cause the cable to hang between the two peaks of the bedforms. Under the actions of ocean currents and internal waves， the suspended section of the optical cable would generate vortex vibrations and even wear due to oscillatory motions with the seabed， so that the safe life of the optical cable would be shorten. Therefore， to determine reasonable length of cable laying is a very important task in the design of submarine optical cable engineering. This article explores the causes of submarine bedforms， the mechanism of cable damage on the bedform seabed， and analyzes the calculation method of cable laying length redundancy in order to provide references for the design of submarine optical cable engineering.