Optical tomography technique is very important in changing conventional techniques for the development of imaging science. It will be applied widely in the fields of biomedical imaging, material structure analyzing and blurry martial target distinguishing etc. In this paper, we introduce the application of a multimode optical fiber sensor in tomography technology. Optic fiber with polished terminations requires the incident ray within a certain angle, so it usually causes deficiency of the light power entered into the optical fiber and diffuse the emergent ray, so polished terminations make it difficult to receive and detect the emergent rays. In order to solve the two problems above, a sphere lens is designed for one termination and a cylinder lens is designed for the other termination. This paper uses mathematics to analyze the relationship between the sphere lens radius, the cylinder lens radius, refractive index of the optical fiber. The relationship between the scanning angles and the numbers of the numbers of the received optical fiber is researched in the air medium, and the designing method for the sphere lens and the cylinder lens are present.