In this article, we propose a fiber displacement sensor based on a few mode fiber loop sandwiched between two single mode fibers (SMF). The proposed sensor is flexible due to the tunable resolution and dynamic range. The FMF is coiled to a fiber loop by making a knot. The in-line MZI sensing structure is fixed on a two dimensional (2D) translation stages. By moving one stage while another stage is fixed, the displacement is applied on the sensing structure. The resolution of the translation stage is 10μm. The few mode fiber loop acts as the transducer for the displacement sensing. The displacement will change the radius of the few mode fiber loop, which leads to a wavelength shift of the interference pattern. When the fiber loop has different initial radius, the same displacement will cause a different curvature variation. So the sensitivity of the wavelength shift to the displacement is dependent on the initial radius. A smaller initial radius of the loop will lead to a larger sensitivity, higher resolution but smaller dynamic range, so it is proper for micro displacement sensing. On the contrary is the lager initial radius that is proper for sensing in a large dynamic range. By simply adjusting the initial radius of the transducer loop, different sensitivity and resolution can be reached. Experimental results show the sensitivities of 0.267nm/mm, 0.384nm/mm, 0.749nm/mm and 1.06nm/mm for initial loop radius of 1.9cm, 1.5cm, 1cm and 0.75cm, respectively.