Wenchang Z oilfield, after 20 years of development,has large differences in reservoir properties between layers. Most production wells adopt joint production methods, resulting in complex distributions of remaining oil. Quantitatively describing the esmaining oil is difficult. Taking the ZJ1-4U oil group in the Wenchang Z oilfield as an example,through details geological description, quantitative description of remaining oil, and time-variable numerical simulation, the distribution of remaining oil was studied in detail, forming a resdarch technique for quantitative description of marine sandstone reservoirs.Through quantitative description, the potential within the oilfield was explored. A scheme for density adjustment is proposed. After production, good results have been achieved, indicating that the quantitative description technique for marine sandstone reservoirs is highly feasible, providing new methods and ideas for similar reservoirs in future exploitation.