In this study, the effect of the TSW (Thrower-Stone-Wales) defects on the mechanical properties of BNNT (Boron Nitride Nanotube) is studied by molecular dynamics simulation using the three different potential models of Dreiding, Tersoff and Reaxx forcefields. To compare the effect of the TSW defect, pristine 5TSW, and 10TSW defected BNNTs are constructed. Assuming that the equivalent continuum structure of BNNT structure is a solid cylinder, the transversely isotropic elastic moduli of each BNNT are determined from tensile, shear, and expansion tests via ensemble simulations. As a result, it is found that the Dreiding forcefield does not describe the degradation of the BNNT by TSW defects while the reactive forcefields of Tersoff and Reaxx forcefield predict a clear degradation in elastic modulus of BNNT.