A cryogenic collimator is needed to test the modulation transfer function (MTF) of the infrared cryogenic camera. The detector of the infrared low temperature camera cannot work normally at room temperature, besides the camera, the off-axis parabolic mirror and the simulated target are spatially separated. So it is necessary to adjust the boresight direction of the camera with the collimator, meanwhile the simulated target must be set on the focal plane and at the 0′ field of the collimator. By using the interferometer, the boresight of the camera and the collimator can be individually elicited to external reference cubes a and b. Based on the direction cosine matrix of the two cubes′ coordination system, the boresight of the camera can be elicited to the direction of the boresight of the collimator. The accuracy of this method is analyzed, and the image of the experiment is also shown. The experimental result shows that the MTF of the camera meets the demand, and it also indicates that the method is reasonable and feasible.