The ray tracing of unclad U-shape multimode fiber optic is examined by using Zemax simulation have been proposed. The influence of the geometry of sensing region such as absorbing medium refractive index, n2, shape of fiber and the bending radius is analyzed. Number of analysis ray is determined and the value of n2 is varied at 1, 1.3314, 1.359, 1.36, 1.37 and 1.4. The intensity of light propagate inside the fiber is reducing at high n2 and this graph pattern is supported by experimental result. A U-shaped sensor is used for the analysis because of the sensitivity is higher than straight fiber design due to their higher penetration depth. Zemax simulation shows that the fiber with bending radius 1.5 mm has higher response compared to fiber with radius 2.5 mm. � 2017 Trans Tech Publications, Switzerland.