Off-axis optical system can meet the needs of focus, FOV and optical distortion, the requirement of the optical system for space-borne off-axis mapping camera can be met well. In view of the strict requirements to the linear array horizontality and consistency of confocal plane for all FOV and all spectral, a method of computer aided adjustment model is proposed for quick alignment and test of the focal plane. Compare the traditional method, this method can both improve the efficiency and achieve high accuracy of alignment and test of the focal plane. The alignment and test result to a type long focal length mapping camera indicate that uniformity of the focal plane for all CCDs less than ±0.05mm and the linear array horizontality less than ±1 ′ .The result shows that this method is feasible and efficient. So it can provide a reference to fasten alignment and test of the focal plane for other space-borne off-axis mapping camera.