A kind of cladding-carved Distributed Bragg Reflection (DBR) fiber laser was proposed for fiber laser refractive index detection. The core sensing unit is a single longitudinal mode dual polarization DBR fiber laser, the beat signal generated by the structure birefringence is used as the sensor signal to detect the refractive index. Frequency coding using in the experiment has the advantages of high sensitivity and is easy to demodulate. Using the thermal effect of the CO2 laser can carve the cavity of DBR fiber laser. The effects of different structural parameters on the sensitivity characteristics were studied by controlling the scanning range and the power of the CO2 laser. The effects of different structural parameters on the sensitivity characteristics were studied. The measured optimum sensitivity is -240 MHz / RI-unit. In addition, the temperature sensing characteristics of the structure were tested, and the sensitivity was increased by 21% to 1.73 MHz/℃, compared to the non-carved structure. The device has the advantages of compact structure, high stability, simple preparation and low cost, and can be used to further study of the sensing and multiplex characteristics of DBR fiber lasers.