The primary hydrocarbon source rocks of Yabei depression in Qiongdongnan basin are coal measures of Yacheng Formation. On the basis of the theory that depositional environment controls the formation of coal measures source rocks, the depositional environments and controlling factors of coal measures source rocks were studied, and the development models of coal measures source rocks were established. The depositional environments of coal measures source rocks were saline-reducing peat swamps of the braided river delta plain and saline-oxidative peat swamps of tidal flat. The controlling factors of coal measures were depositional environments which governed the abundance and types of organic matters, microscopic constituents, and thickness of coal measures, paleo-climate which provided material background for the development of source rocks, sea level which controlled the distributive characteristics of coal measures within the strata and the perversion condition, and paleo-structure which determined formation and evolution of specific basins. There are two development models of coal measures source rocks of Yacheng Formation in Yabei depression: one is peat swamps of tidal flat in which the reduction played the leading role; the other is peat swamps of the braided river delta plain in which the high productivity was the most effective factor.