The multimode-fiber modal interferometric sensor has been the research focus in the fiber optic sensor field in virtue of its simple structure, low cost, lightweight, high sensitivity, excellent degree of integration, and resistance to electromagnetic interference. It is widely applied to safety monitoring in large-sized architectures for measurement of such physical parameters as stress, temperature, vibration, and displacement. Early fiber optic modal interferometric sensors are mainly based on the reflective Michelson interferometer and the Mach-Zehnder interferometer. The single-mode fiber and the multimode fiber are used as the sensing fiber. Mode coupling is achieved by the fusion splicing of different fibers. Modal interferometric sensor can be used to measure refractive index, concentration and magnetic field etc. by etching the sensing fiber and coating the fiber with corresponding sensitive material. The fabrication of fiber optical modal interferometric sensor mainly depends on fiber fusion methods and fiber types, as well as the optimization of fiber physical parameters. The progress in the multimode-fiber modal interferometric sensor at home and abroad is reviewed, and the merits and drawbacks are analyzed.