The Global Navigation Satellite System (GNSS) is an important mean of implementing Performance Based Navigation (PBN). Satellite Based Augmentation System (SBAS) augment GNSS to meet the high integrity requirement of civil aviation. This paper introduces the concept and principle of SBAS. Taking Wide Area Augmentation System (WAAS) as an example, the system architecture, data processing flow, system operation and management as well as system application and service are introduced in detail. The method of SBAS in civil aviation application is analyzed. The development trend of using DFMC SBAS to realize CAT-I precision approach and the trend of applying SBAS service in other industries are indicated.