A single-mode fiber surface plasmon resonance refractive index sensor based on U-shaped structure was designed. The sensor is fabricated by coating the gold nanometer layer and the TiO2 modulation layer on the surface of single-mode optical fiber whose cladding is partiallyremoved and then isbent into U-shape. The impact of different bending radius and thickness of TiO2 on the sensing performance was studied by using finite element simulation software COMSOL Multiphysics. Through analyzing four different bend radii(R=0.3 cm,0.5 cm,0.8 cm,1 cm), we found that with the increase of the bending radius, the surface plasmon resonance signal intensity increases and the peak shifts to shorter wavelength slightly. The performance of the sensor with different thickness of the TiO2 modulation layer from 0 to 40 nm was studiedunder the condition of bending radius of 0.5 cm. With the increase of the thickness of the TiO2 modulation layer, the surface plasmon resonance peak shifts to longer wavelength and the sensitivity of the peak to the analyte refractive index increases significantly. The sensitivity of the sensor in the low refractive index region (nd=1.333) reached 5 959 nm/RIU and the sensitivity of the high refractive index region (nd=1.383) reached 11 092 nm/RIU at the bending radius of 0.5cm and the thickness of the TiO2 modulation layer was 40nm. Compared with the results of no modulation layer, the sensitivities increase by about doubled.