To enhance sensor integration and align with the trend of device miniaturization, a compact fiber optic probe based on a fiber Bragg grating-Fabry-Perot (FBG-FP) cascaded structure is proposed and fabricated for monitoring refractive index and temperature in biological fluids. By constructing a cascaded structure reflectivity distribution model, the device cascade sequence is optimized. The fiber FP probe with a single-mode fiber-hollow-core fiber-single-mode fiber structure is prepared using precise cutting and splicing techniques. A FBG is inscribed 100 μm from the splicing interface using femtosecond laser direct writing, achieving a cascaded compact dual-sensing element fiber optic probe. The wavelength/intensity response characteristics of the FBG and FP structures to temperature and refractive index effectively resolved the cross-sensitivity issue in principle. A temperature and refractive index experimental system is set up to analyze the sensing characteristics of four fiber optic probes within a temperature range of 25℃ to 55℃ and a refractive index range of 1.333 0 to 1.381 6. Experimental results show that, during temperature cycling, the FBG and FP central wavelengths redshifted with increasing temperature and blueshifted with decreasing temperature, with average temperature sensitivities of 9.36 and 8.52 pm/℃, respectively. As the ambient refractive index increased, the FBG wavelength and intensity are unchanged, while the FP interference wavelength stays constant and the resonance intensity gradually decreases, with the intensity fitting results showing a parabolic trend. Segmented linear fitting with a refractive index of 1.354 6 as the boundary reveals that within the refractive index range of 1.333 0 to 1.354 6, the FP sensitivity averaged 5.86 dBm/RIU with a maximum of 10.72 dBm/RIU, and within the range of 1.354 6 to 1.361 8, the FP sensitivity averaged 1.40 dBm/RIU with a maximum of 2.74 dBm/RIU. This sensor, characterized by its simple fabrication, compact structure, and high sensitivity, shows promising application prospects in the field of biological fluid monitoring.