A theoretical model for the backscattering from thin film deposited on super-smooth optical surface is established, based on which, a solid-angle integrated scattering (SIS) characterization system is built. The SIS measurement collects backscattered light in a limited solid angle by using an integrating sphere. The characterization system consists of three major parts: mechanical system, photoelectric conversion system, and control software. The scattered flux is spatially integrated by the integrating sphere and is detected by a photomultiplier and lock-in amplifier. The lock-in detection offers excellent noise rejection and is the key to the sensitivity. The measurement can be performed completely under the control software based on the Labview. Experiment results of the measurement are presented, sources of error are analyzed. Results showed that the backscattering down to 10ppm could be characterized with a resolution of 1ppm. The system can be used to measure the backscattering for an incident angle between 25<sup>o</sup> and 50<sup>o</sup>.