The invention discloses an NtJAZ1 gene mutant capable of improving nicotine content of tobacco leaves and application of the NtJAZ1 gene mutant. The nucleotide sequence of the NtJAZ1 gene mutant capable of improving nicotine content of tobacco leaves is shown as SEQ ID NO: 3, and compared with an NtJAZ1 gene with the nucleotide sequence shown as SEQ ID NO: 1, the NtJAZ1 gene mutant capable of improving nicotine content of tobacco leaves has c.383C > T mutation. According to the NtJAZ1 gene mutant capable of improving the nicotine content of the tobacco leaves and the application thereof, the NtJAZ1 gene mutant capable of improving the nicotine content of the tobacco leaves is provided for the first time, the nicotine content of the tobacco leaves of the NtJAZ1 gene mutant plant capable of improving the nicotine content of the tobacco leaves is improved by about 40% compared with that of a control group, the nicotine content of the tobacco leaves is remarkably improved, and the production cost of nicotine raw materials is reduced.