A separation type fiber sensor structure is designed to improve sensitivity, in which double Fabry-Perot (F-P) cavities with similar cavity lengths are connected in parallel. The sensitization principle of this structure is theoretically analyzed and two groups of sensitizing structures are prepared. The experimental results show that the pressure sensitivity of the sensitizing structure is increased to 43.95 nm/MPa from 4.85 nm/MPa of the single F-P structure. The temperature sensitivity is increased to 0.40364 nm/℃ from 0.0675 nm/℃ of the single F-P cavity. At the same temperature, the use of double cavity structure can eliminate the effect of temperature cross-sensitivity on measurement results. The structure overcomes the defects of integrated sensitization structure, and increases the sensitivity without affecting the original sensor structure. The sensitivity can be adjusted by replacing the auxiliary cavity. This structure has the advantages of good portability and small cross-sensitivity, etc.