Aluminum is the primary structural material in nuclear engineering, and its cross section induced by 14-MeV neutrons is of great significance. To address the issue of insufficient accuracy for the [Math Processing Error]27Al(n,2n)[Math Processing Error]26Al reaction cross section, the activation method and accelerator mass spectrometry (AMS) technique were used to determine the [Math Processing Error]27Al(n,2n)[Math Processing Error]26Al cross section, which could be used as a D-T plasma ion temperature monitor in fusion reactors. At the China Academy of Engineering Physics, neutron activation was performed using a K-400 neutron generator produced by the T(d,n)[Math Processing Error]4He reaction. The [Math Processing Error]26Al/27Al isotope ratios were measured using the newly installed GYIG 1 MV AMS at the Institute of Geochemistry, Chinese Academy of Sciences. The neutron flux was monitored by measuring the activity of [Math Processing Error]92mNb produced by the [Math Processing Error]93Nb(n,2n)[Math Processing Error]92mNb reaction. The measured results were compared with available data in the experimental nuclear reaction database, and the measured values showed a reasonable degree of consistency with partially available literature data. The newly acquired cross-sectional data at 12 neutron energy points through systematic measurements clarified the divergence, which has two different growth trends from the existing experimental values. The obtained results are also compared with the corresponding evaluated database, and the newly calculated excitation functions with TALYS[Math Processing Error]−1.95 and EMPIRE[Math Processing Error]−3.2 codes, the agreement with CENDL[Math Processing Error]−3.2, TENDL-2021 and EMPIRE[Math Processing Error]−3.2 results are generally acceptable. A substantial improvement in the knowledge of the [Math Processing Error]27Al(n,2n)[Math Processing Error]26Al reaction excitation function was obtained in the present work, which will lay the foundation for the diagnosis of the fusion ion temperature, testing of the nuclear physics model, evaluation of nuclear data, etc.