A two-dimensional large-strain quasi-distributed fiber optic sensor based on an integrated polymer flexible film with a fiber grating array has been proposed and developed to address the technical challenges of existing fiber optic sensing equipment, which struggles to simultaneously achieve two-dimensional vector strain identification, large deformation range detection, and multi-point quasi-distributed measurement. This sensor integrates the fiber grating array orthogonally onto the surface of a highly malleable polymer film substrate, combining the excellent mechanical tensile properties of the flexible film to overcome the limitations of traditional fiber optic sensors, such as small strain measurement range, single measurement dimension, and inability to identify the direction of strain vectors. The sensor mechanism has been studied, and sensor samples have been prepared. Test results show that the sensor can achieve multi-point distributed measurement of a two-dimensional large-strain range of at least 0–10% in both the X- and Y-directions, with excellent linearity and repeatability. The sensor has a simple structure and strong flexible conformability, providing new technical support for precise testing of two-dimensional global strain fields and engineering applications of flexible sensing technology.