Abstract: During the 1:250000 geological survey of the Qionghai County Sheet, a suite of early-mid basic volcanic rocks exposed on northern Hainan Island was studied intensively and the Duowen Formation was established. This formation is divided into the upper and lower members, which represent basic lavas and pyroclastic rocks formed from the late part of the early Pleistocene to the early part of the middle Pleistocene and in the mid-late part of the middle Pleistocene. It is distinguished from the Daotang and Shishan formations by its lower stratigraphic position and lithologic association. This paper summarizes the distribution, lithology, lithofacies, age and geochemistry of the formation and discusses its tectonic environment.