AbstractThe climatic suitability and driving climatic factors of forage crops are considered fluctuant, and their measurements are important for the production of high‐quality forage under the context of global climate change. Meanwhile, need for improving the domestic supply of high‐quality forage sources is increasing in the related parties of forage and livestock production in Korea. Therefore, this study analyzed the climatic suitability conditions of whole crop maize (Zea mays L.) and sorghum–sudangrass hybrid (Sorghum bicolor × Sorghum sudanense) in the south area of the Korean Peninsula and Jeju Island. Furtherly, the driving climatic factors on the two summer forage crops were detected through stepwise regression analysis based on historical field experiments and climatic data. The results showed that the climatic conditions in almost all the areas of the south area of the Korean Peninsula and Jeju Island are suitable or moderately suitable for the cultivation of the two forage crops except some mountainous areas. However, since the precipitation in this region is concentrated in the growth period of the two forage crops, the accumulated precipitation was detected stressful on their yields.