International trade has been considered a critical driving force of material flows and their environmental pressures, which has been a global research hotspot. The United Nations Commodity Trade Statistics Database (UN Comtrade) is the original and probably the most widely-used data source to support the physical trade analysis. However, data discrepancies have been discovered in UN Comtrade, which may lead to diametrically conflicted conclusions if not properly addressed. To promote applications of UN Comtrade, this article reviews data statistics criteria and preprocessing procedures, discusses three main data quality issues (outliers, missing values, and bilateral asymmetries), and reviews methods to explore adequate options. It is revealed that data quality issues existed in data of almost all the commodities, reporters, and periods, but existing methods are subject to certain limitations. Furthermore, this article presents a brief introduction of our following work on addressing these issues.