Abstract: To understand responses of Chamaecrista rotundifolia to planting density, the effect of five planting densities (5, 10, 20, 30, 40, 50 plants/m²) on yield, economic characteristics, crude protein and photosynthetic characteristics of C. rotundifolia were studied. There was an initial increase then a decreasing trend with increasing plant density. Yield of fodder reached a peak value at a planting density of 40 plants/m², and yield of hay reached a peak value at 30 plants/m². Crude protein contents of C. rotundifolia were distributed more in leaves than in stems. Crude protein contents initially increased and then decreased with increasing planting density, and reached the peak value at a density of 30 plants/m². The net photosynthetic rate of C. rotundifolia at different planting densities was due to non-stomatal limitation. Synthesize evaluation showed that a planting density of 30 plants/m² gave the highest hay yield of 3 454.83 kg/hm² by C. rotundifolia, and the crude protein production reached 625.83 kg/hm².