Based on the distributed optical fiber measurement method of optical frequency domain reflection （OFDR）， the conversion relationship between the strain measured by optical fiber and the horizontal displacement of soil based on Euler beam theory was proposed， which was verified by indoor experiments. The feasibility of the distributed optical fiber measurement of horizontal displacement and the accuracy of the strain-displacement transformation relationship were verified. The optical fiber measurement method was applied in a foundation pit project. Through the test， the optical fiber measurement method was testified to be able to accurately measure the horizontal displacement of deep soil in the process of excavation.