Based on the vector wavefront aberration theory, the field curvature characteristic of the off-axis three-mirror optical system under a small misalignment during installation and adjustment was analyzed. A method for generating field curvature by tilting the focal plane to compensate for system misalignment is proposed. The simulation analysis was conducted using a remote sensing camera. Besides, the relationship between the number of split field-of-view of focal plane and the tertiary mirror installation accuracy requirements was analyzed, and the optical system alignment process and method were given. Then, the field curvature characteristic of the camera was tested by measuring the modulation transfer function, and the focal plane inclination angle was corrected to compensate for the curvature aberration. After the correction, the modulation transfer function of the edge field-of-view significantly improved. The modulation transfer function of each field-of-view of the camera is greater than 0.21.