Grain products are essential for human survival and economies, and their price fluctuations significantly impact global economic stability. Recent frequent uncertain events have made global economic policy uncertainty a major factor in global food price fluctuations. This study choose European debt crisis, the COVID-19 pandemic, and the Russo-Ukrainian war as three typical type of uncertainty event. And used TVP-VAR-SV model to examine the impact of global economic policy uncertainty on the prices of beans, maize, rice, and wheat. The result shows policy uncertainty leads to fluctuating grain prices, with food grains (rice, wheat) and feed grains (beans, maize) reacting differently. And different types of uncertainty events have different effects, with the pandemic having the greatest effect. Finally, the paper suggests strategies for global food security, including improved information communication, policy control, early warning systems, stable economic policies, and supervision of the agricultural futures market.