In this study, we present a side-grinding method to make U-shaped optical fiber sensor. The plastic optical fiber of diameter 1000/980 μm is used to fabricate U-shaped optical fiber sensors by mini-grinder. The side-grinding depth of U-shaped optical fiber sensor is controlled by accurate moving stages. A designed fiber fixture is used not only to fix fiber during side-polish but also to stabilize the specimen. The specific side-polish depth is two fifths core diameter. The high-power green LED with wavelength 528nm is employed as incident light for the fiber sensor detection, and sucrose solution as specimen with refractive index of 1.333 to 1.403 is tested by fiber sensor to confirm the detecting ability of U-shaped optical fiber sensor. The results showed the side-grinding system can make U-shaped optical fiber sensor with low depth error. The designed fiber fixture can fixed the specimen to increase the stability of fiber sensor. The best of sensor resolution of grinding depth on sensing area is 428.5 μm, and the best of sensor resolution is 2.18×10-4.