The utility model discloses a distributed optical fiber measurement system for monitoring whole-section horizontal displacement of a dam body. A deformation monitoring pipeline perpendicular to the axis of a dam is embedded into the dam and formed by connecting a plurality of sections, an expansion pipe joint is arranged on each section, and an anchor plate for each expansion pipe joint is fixed in the dam body; and a sensing optical fiber is arranged in the middle of the inner part of the deformation monitoring pipeline. The system is characterized in that the sensing optical fiber is fixed and tensioned by an optical fiber fastening and pre-tensioning device; two kinds of different optical fibers are arranged in the sensing optical fiber, wherein one kind of fastened and stressed strain optical fiber is directly protected by a jacket and used for measuring the displacement change of the dam body, and the other kind of loosened and un-stressed temperature optical fiber is protected by a plastic casing and used for measuring the temperature change of a position where the optical fiber is located to realize temperature compensation; and both the strain optical fiber and the temperature optical fiber are connected to a distributed optical fiber acquisition instrument. The measurement precision of the system is 0.2%F.S, so the measurement precision is high, the accuracy of a monitoring system is ensured, and the requirement for monitoring the horizontal displacement in an earth and rockfill dam is met.