The photosynthetic indexes of Echium vulgare L.leaves were determined using LI-6400 XT Porta-ble Photosynthesis System with the density treatment of 5 cm, 10 cm, 15 cm, 20 cm and 25 cm. The results showedthat all the treatments appear photosynthetic midday-depress except the density of 20 cm. Midday-depress ap-peared in the morning at larger density and appeared in the afternoon at small density, which appeared at 10 o’clockin 10 cm, appeared at 12 o’clock in 5 cm, others at 14 o’clock. The maximum photosynthetic rate was 21.467 μmol·m^-2·s^-1, the minimum was 18.86 μmol·m^-2·s^-1, and the average was 20.392 μmol·m^-2·s^-1. From the analysis of pho-tosynthetic midday-depress, the optimum planting of Echium vulgare L. was 20 cm. Density affected photosynthesisdiurnal variation of Echium vulgare L., that was the direct factor influencing crop yield. Only at the density of 25 cm, the correlation between net photosynthetic rate and transpiration rate and stomatal limitation appeared, the cor-relation coefficients were 0.94, 0.93 and 0.95. Net photosynthetic rate appeared significantly correlated with inter-cellular CO₂ concentration, correlation coefficients was 0.92. It appeared highly significantly negative correlated to water use efficiency and mesophyll conductance, correlation coefficients was-0.97,-0.92. Correlation did not reachsignificant level at other density, it indicated that the optimum planting density was 25 cm.