The problem of nicotine to nornicotine conversion is severe in Burley production in Sichuan, which is a fast growing Burley producing area in China. The improvement on the trait of nicotine conversion for a series of Burley hybrids was conducted through early identification, selection and hybridation of non-converter parent plants, and the effects of harm reduction and quality enhancing were evaluated for the improved hybrids Dabai1NN, Dabai2NN, Dabai3NN, compared with the regular hybrids. The selection was conducted by using early ethryl stimulation and identification methods for the parent population. Through 3 generation systemic selections, the proportion of converters in the population of Dasuo26 (male parent of Dabai 1 and Dabai 2) and Dasuo27 (male parent of Dabai 3), both of which were main contributors of converting genes to the relevant hybrids, reduced to less than 5% and less than 9%, respectively, from 53.2% and 96.0% in the original population. The proportions of total converters in the 3 improved hybrids were 4.65%, 4.76% and 6.52%, respectively, 80.1%, 61.9% and 91.7% lower than the regular hybrids, and the newly emerged converters were mostly low converters. The nicotine conversion rates of the 3 improved hybrids in the bulk samples were 3.0%, 2.2% and 2.63%, respectively, 72.5%, 71.1% and 94.9% lower than the regular hybrids, respectively. The total TSNA contents in the 3 improved hybrids decreased 38.5%, 29.2% and 50.8% compared with regular hybrids, and the difference was mainly caused by NNN reduction, with the decreasing rate of 61.3%, 49.6% and 71.0%, respectively. Improved hybrids had better tobacco flavour quality than the regular hybrids, with increased Burley style, increased aroma quality and quantity, and decreased offensive odour. The blended cigarettes made from improved Burley tobacco had more reasonable alkaloid composition, higher flavour quality and lower TSNA delivery in the smoke. In addition to the selection of non-converters in the selfing lines of non-converter plants, we also selected newly emerged low converters and planted their selfing lines in the next generation, and high converters were found produced from low converter lines; this result proved that converters can come from non-converter line and the degree of conversion level can accumulate and increase through generations.