Broomcorn millet (Panicum miliaceum L.) is a minor crop within the same genus as the bioenergy crop switchgrass (Panicum virgatum L.). It is one of the oldest cultivated crops and it plays important roles in both food and culture in China. Its wide distribution and long history of cultivation have led to the accumulation of abundant genetic resources. Here, we introduce briefly the history and related culture of the crop and review the diversity of the crop for agronomic traits among the germplasm collections in China and recent developments in genetic diversity analysis. It will be helpful for facilitating further research on broomcorn millet.