The invention discloses an optical
system for a space astronomical observation infra-red
telescope, which comprises a reflection-type focal-free main optical
system (1), a single-axis
scanning mirror (2) and a subsequent imaging optical
system (3), wherein in the reflection-type focal-free main optical system (1),
ray is incident into a reflexing mirror (6) via an eccentric light through hole after being successively reflected by a main mirror (4) and a
secondary mirror (5), and is reflected into the single-axis
scanning mirror (2) successively by the reflexing mirror (6) and a
prism (7); the single-axis
scanning mirror (2) ensures that the aiming line of the optical system of the space astronomical observation infra-red
telescope is constant by one-dimensional linear scanning; the incident
ray of the reflection-type focal-free main optical system (1) is reflected to the subsequent imaging optical system (3); the subsequent imaging optical system (3) comprises an off-axis reflection
type system, a color separation filter and a focal plane; the off-axis reflection
type system corrects the aberration of the reflection-type focal-free main optical system (1); and the emergent
ray of the reflection-type focal-free main optical system (1) is divided into two or more than two spectral channels by the color separation filter to be imaged to a corresponding focal plane.