Neoclassical tearing modes (NTMs) of m = 2, n = 1 induced by sawtooth crashes in tokamak plasmas are studied based on the results of HL-2A tokamak experiments. A model of sawtooth-driven Δ' for NTMs due to the toroidal coupling effect is proposed and applied to the observed growth of 2/1 islands with the sawtooth oscillation observed in the HL-2A experiment. The neoclassical tearing island growth is calculated based on the model and the result is found to be in good agreement with experimental data.