The Export Coefficient Model (ECM) has been widely used to estimate nonpoint source (NPS) pollution loads due to its ease of application. Accurate pollution export coefficients are crucial for reducing uncertainties in load estimation. By integrating artificial simulated rainfall experiments with field survey data, we have developed a new method that estimates regional pollution export coefficients. Results showed that the export coefficients calculated using this new method accurately express the regional rainfall-runoff characteristics, as the simulation precision of this method had grown by 30% than the results with traditional ECM and export coefficients which surveyed from the literature. Based on the calculated regional pollutant export coefficient, the annual loads of TN and TP in the plains area of the Baiyangdian basin in 2010 were 25,967.13 t and 4349.29 t, respectively. Among different types of sources, rural livestock had the greatest contribution (over 60%), whereas rural domestic waste represented the smallest contribution (approximately 10%). Of the different sources, pigs contributed almost half of all NPS pollution from livestock, rural residential areas were the main land use pollution source, and rural living garbage was the main source of rural domestic waste. Spatially, NPS was mainly distributed in the Zhulong and Juma watersheds. Other watersheds only contributed approximately 5% NPS per watershed. However, the per-area loads of these lower load watersheds were larger or nearly equal to that of the Zhulong watershed. Therefore, the lower load watersheds should be addressed for the control of NPS pollution.