【Objective】 The combination of planting pattern and planting density was one of the effective ways to increase the utilization rate of light energy and to increase the yield of crops in dryland farming area, which was of great significance in dryland agricultural production. The effects of different planting densities and planting modes on the structure of sorghum canopy were studied to provide a theoretical basis for further excavating the yield potential of sorghum in the semi-arid region of western Liaoning. 【Method】 The brewed sorghum variety Liaoza 19 was used as the experimental material. Two factors split plot design was used to examine the effects of different treatments on photosynthetic characteristics of the population and yield by analyzing plant shape index, photosynthetic physiological indexes, and aboveground biomass. The main area was planted with 60 cm equal row spacing (P1) and 80 cm+40 cm wide-narrow row planting (P2), and the split area was planting density with 75 000 plants/hm 2(D1), 105 000 plants/hm 2(D2), 135 000 plants/hm 2(D3) and 165 000 plants/hm 2(D4). The experiment was repeated three times. 【Result】 In the two years, grain yield of sorghum was in turn D3>D2>D4>D1 from big to small under the same planting pattern. The average 2-year yield of P2D2 was 5.02% higher than that of P1D2, and that of P2D3 was 6.96% higher than that of P1D3, and that of P2D1 was 0.27% lower than that of P1D1, respectively. The yield of P2D4 was 2.55% lower than that of P1D4 in 2017. The yield of P2D3, which was the highest in all treatments, was 10 267.14 kg·hm -2. In accordance with the increase of planting density, the plant height, population leaf area index and leaf orientation value showed an increasing trend, while stem diameter, stem diameter coefficient, leaf area per plant, angle between leaf and stem, light transmittance, SPAD value and net photosynthetic rate decreased. The wide-narrow row planting had the advantages in the aspects of stem diameter coefficient, group leaf area index, light transmittance, net photosynthetic rate, SPAD value compared with equidistant row planting under D2 and D3. P2D2 increased by 2.80%, 3.17%, 16.33% compared with P1D2 and P2D3 increased by 9.29%, 7.27%, 17.57% compared with P1D3 respectively in the aspects of mean stem diameter coefficient, mean population leaf area index and mean net photosynthetic rate in the two years. In the stage of flowering and milking, P2D2 increased by 22.55%, 15.81% compared with P1D2, respectively, and P2D3 increased by 37.45%, 102.09% compared with P1D3 in the aspect of mean light transmittance at the bottom, respectively, and P2D2 increased by 38.72%, 8.16% compared with P1D2, respectively, and P2D3 increased by 56.59%, 93.60% compared with P1D3 in the aspect of mean light transmittance in the middle of the canopy, respectively, in the two years. In the stage of flowering and milking, P2D2 increased by 6.46%, 5.41% compared with P1D2, respectively, and P2D3 increased by 8.75%, 5.46% compared with P1D3 on two years' average SPAD value, respectively. Under the density of D2 and D3, the upper leave of the wide-narrow row planting was relatively straight and leaf area was lesser, which could improve the light receiving condition of the middle and lower leaves, the lower blade was relatively flat and leaf area was larger, which could reduce the loss of light leakage and improve the utilization ratio of light energy compared with equidistant row planting in the two years. 【Conclusion】Appropriate increase of planting density was the key to increase sorghum yield. Under optimum planting density, wide-narrow row planting, which was an important way to realize the synergistic gain and yield enhancement of crop population structure and plant individual function, could effectively improve canopy light transmittance, increase population leaf area index, expand photosynthetic area, and improve the photosynthetic performance of the leaves, especially the middle and lower leaves.
