This study examines the impacts of China’s exchange rate policy on commodity market with a lengthy vertical supply chain. By taking the soybean industry as a case, the analysis considers the joint effects of the undervaluation of the RMB/$US exchange rate and the interactions along vertical supply chain relative to prices, supplies, demands, and trade of world soybean and soybean products, In the analysis, the effects of China’s monetary policy of RMB undervaluation on world soybean, soybean meal and soybean oil supplies, demands, prices and trade over the 1993/94 through 2012/13 are measured. Simulation results show RMB undervaluation has significant effects on world soybean and soybean products markets. China’s monetary policy of RMB undervaluation is likely to increase China’s soybean price and reduce China’s soybean imports. It is also found that China has borne most of the burden from its own exchange rate undervaluation policy over the years.