The invention discloses a refrigerating type infrared focal plane detector back face thinning method. The method comprises the steps that a refrigerating type infrared focal plane detector is roughly machined into the first preset thickness through a diamond cutting machine; and furthermore, the refrigerating type infrared focal plane detector roughly machined to the first preset thickness through the diamond cutting machine is finely machined to the second preset thickness. Back face thinning is carried out on the refrigerating type infrared focal plane detector through diamond cutting, and due to the fact that a smooth diamond point can enable the machined surface to have the minimum residual stress and the ideal roughness and meanwhile clamps are not involved, when devices of different sizes are cut, pressure and other technology parameters do not need to be designed again. Thus, the machining method is simple, the machining technology is controllable, and therefore the problem that in the prior art, the technology for back face thinning of the refrigerating type infrared focal plane detector is low in efficiency is effectively solved.