A double-loop desensitization structure is designed. The finite element analysis of the 26 mm long desensitization substrate is carried out. The tensile and compressive displacements of 0.065 mm are applied to the left and right ends of the desensitization substrate, respectively. The simulation result shows that the desensitization ratio of the desensitized substrate is about 3.5 and the strain measurement range can reach ±5000 με. The desensitization substrate can be operated within the elastic range of the material without affecting the service life of the sensor. The tensile test of fiber Bragg grating (FBG) with double-loop desensitization structure in the range of 500 με shows that the linearity of the sensor is over 0.999, and the full scale accuracy is about 0.1%. The sensor can achieve real-time accurate online monitoring, rapid system data acquisition, and high reliability. It is expected to be applied to the situations where the larger strain range of key structures is needed to be measured, such as ships, bridges, aircraft, and so on.