Roots are important for the nutrition absorption of Flue-cured tobacco. In this study, by changing the amount of biochar in the soil, the effects of biochar on root system development, leaf photosynthetic characteristics, and physiological parameters of the coordinated growth of the aboveground and underground of flue-cured tabacco were investigated. A field experiment was carried out in 2015 and 2016, and there was six treatments, i.e. CK, T1, T2, T3, T4, and T5. Compared with the conventional fertilization, the nitrogen fertilizer application rate of each treatment was decreased by 40%. In the key growth period of flue-cured tobacco, root system growth characteristics and leaf photosynthetic characteristics were determined. The results showed that biochar application at 2 400 kg/hm2 increased root vigor by 177.8%, total root area by 91.35%, the total root tip number by 100.9%, leaf area by 73.29%, chlorophyll relative value by 57.68%, net photosynthetic rate by 77.32%, and leaf area coefficient by 23.48%, respectively. Biochar could effectively promote the growth and development of the root of flue-cured tobacco, optimize root physiological parameters, and improve leaf photosynthetic physiological and leaf development parameters through the improvement of root development, with the improvement effects of biochar ranching a peak in T4.