A novel 3-dimensional fiber Bragg grating (FBG) strain and displacement sensing system based on a cylinder structure was proposed. Three FBGs, fixed in the outer surface of the cylinder at the same level according to a 120° angle interval, were used as sensing elements. In principle, the three FBGs have some fixed relationship when a strain F is put on the cylinder. Based on the principles of physics and mathematics, theoretical derivations and the experimental set-up were shown. According to the experimental results, this sensor could measure the size and angles of the strain or displacement accurately.