A cladding mode resonant specialty optical fiber comprising a double cladding structure is proposed. The specific fiber has a thin and low refractive index inner cladding. Based on the coupled mode theory, a core mode can be resonantly coupled to a cladding mode, and then a band-reject spectrum can be obtained. We mainly introduce the fabrication technology, operation principle of the specific fiber and demonstrate its senor applications in bend, solution refractive index (RI) and RI/temperature dual parameters. As the theoretical and experimental results show, the specific fiber is sensitive to the parameters of bend and solution RI. Moreover, the temperature sensitivity of the specific fiber can be adjusted by different dopants in the inner cladding.