Utilizing simultaneous measurements of sea surface wind speed from the Chinese HY-2 satellite scatterometer and significant wave height from its altimeter, the wind-sea and swell in the South China Sea (SCS) for the period 2012-2013 were characterized, based on a statistical-based swell probability (SP) index and a physical-based wave age (WA) index. The two indexes were higher in the central sea (SP > 0.5, WA > 1.4), where mixed wave conditions dominate, while the wind-sea was more common (SP < 0.3, and WA < 1.2) in offshore regions, which include the Beibu Gulf, the area southwest of Taiwan island and the region between Vietnam and the Nansha islands. Seasonally, the indexes showed maximum values in spring, and the seasonal variabilities in the northern (latitude > 17 degrees N) and southern SCS (latitude < 12 degrees N) were more prominent than in the middle SCS. These results may have practical applications in coastal engineering design, wave forecasting and various sea going activities.