The stereo mapping precision of mapping cameras depends on the calibration precision of the geometric parameters, such as inner orientation parameters and distortion, therefore, a new calibration method of inner orientation parameters and distortion for a three-mirror off-axis Time Delay Integration(TDI)CCD camera was proposed. The optical system and image plane stitching of the camera were introduced, and the meanings of the inner orientation parameters and distortion were defined. A calibration system and corresponding mathematical model were established, then the expressions of inner orientation parameters and distortion were settled by the least square poly-regress method. A calibration experiment was performed on the camera, and results show that the point calibration accuracy and the focal calibration accuracy are better than 1.0 μm(1σ) and 2.0 μm(1σ), respectively.Moreover, the distortion calibration accuracy has been 2.3 μm(1σ). Obtained results demonstrate that the calibration method has the advantages in the speed and efficiency for three-mirror off-axis TDICCD cameras.