The size and structure of a three-line array stereoscopic mapping camera are mainly determined by its optical system. To realize the miniaturization, lightening and high reliability of the camera,several kinds of optical system configurations,refraction,reflection and refracting-reflecting optical systems, are analyzed and compared by the requirements of the optical system. In accordance with the environment adaptability and structure layout of the camera,a telecentric system is adopted to design a new optical system to meet the requirement of stereoscopic mapping. The MTF value of each lens in designed optical system is close to the diffraction limit at Nyquist frequency of 77 lp/mm. The distortion of each optical system is less than 2.4×10-5 for the forward and backward sight cameras and 2×10-5 for the straight-sight camera.The tested result shows the MTF of each optical system can reach 0.43 at Nyquist frequency of 77 lp/mm, which is 0.2 higher than a static MTF in laboratory and meets the requirements of the mapping camera for precision.