An optical assembly, designed for the cold atomic clock of space experiment, is described. This optical system is used for atomic cooling, moving molasses, state preparing and clock signal detecting under microgravity environment in space. Distributed Bragg reflection (DBR) lasers has been firstly used in laser cooling of 87Rb atoms in space. All the optical and mechanical components are integrated in a 300 mm × 290 mm × 10 mm aluminum silicon carbide baseplate. Comparing with the conventional optical systems for laser cooling, the system is more compact, more robust and miniaturized. This optical setup has operated for about one year in fountain clock, ground tested by the rigorous tests of thermal and mechanical vibration, keeping high performance with no alignment needed.