Abstract: 【Objective】 This study aimed to investigate the effects of different application rates of a slow and controlled release integrated fertilizer on carbon， nitrogen， and lipid metabolism in flue-cured tobacco， thereby providing reference for applying slow and controlled release integrated fertilizer in tobacco production. 【Method】 The flue-cured tobacco variety Yunyan 97 was used as the test material. Three treatments of slow and controlled release integrated fertilizer application rates were established： 750 kg/ha （T1）， 1500 kg/ha （T2）， and 2250 kg/ha （T3）， with conventional fertilization as the control （CK）. After 70 d of transplantation， middle leaf samples were collected from treatments to observe cellular ultrastructure， measure the contents of starch， reducing sugar， total sugar， nitrogen， and fatty acids， and determine the relative expression of key genes of carbon， total nitrogen， and lipid metabolism. The economic traits of cured tobacco leaves were measured. 【Result】 The contents of starch， reducing sugar， and total sugar in cured tobacco leaves followed the order of T3 > T2 > CK > T1. With increasing application rates of slow and controlled release integrated fertilizer， the contents of starch， reducing sugar， total sugar， and total nitrogen in tobacco leaves of T1， T2， and T3 treatments gradually increased. The relative expression of glucose pyrophosphorylase gene （NtAGP）， sucrose invertase gene （NtINV）， starch synthase gene （NtSS）， starch debranching enzyme gene （NtDBE）， α-amylase gene （NtAMML-α）， nitrate transporter gene （NtNRT2.5）， nitrate reductase gene （NtNIA1）， and ammonium transporter gene （NtAMT2） gradually increased， whereas the relative expression of granule-bound starch synthase gene （NtGBSS1） gradually decreased. The carbon-nitrogen ratio （C/N） was in the order of T2 （17.37） > T1 （16.13） > CK （15.90） > T3 （12.94）， with significant differences between treatments （P<0.05， the same below）. Compared with CK， the contents of linolenic acid， linoleic acid， oleic acid， and palmitoleic acid， as well as the relative expression of lipid transfer protein gene 2 （NtLTP2）， MYB transcription factor gene （NtMYB106）， and wax synthesis gene 10 （NtCER10） were reduced in T1， T2， and T3 treatments， with the T2 treatment showing the most pronounced decreases for key genes of lipid metabolism. Economic trait statistics revealed that the T2 treatment achieved the highest yield， average price， output value， and proportion of medium and high quality tobacco leaves， indicating the best overall performance. 【Conclusion】 Applying slow and controlled release integrated fertilizer at 1500 kg/ha effectively promotes nitrogen uptake， transport， and assimilation in tobacco plants， coordinates the C/N， and effectively reduces the content of unsaturated fatty acid in cured tobacco leaves， thereby improving both leaf quality and economic traits in tobacco leaves.