The excitation mechanism and stabilization of the observed m/n = 1/1 instability during the sawtooth ramp phase in the lower hybrid current driven plasmas on the HT-7 tokamak (Sun Y et al2005 Plasma Phys. Control. Fusion47 745–56) have been investigated in this paper. This mode is most likely destabilized by the current density gradient at the q = 1 surface. Based on the local transport model, it is shown that the saturation and stabilization of the m = 1 mode before the subsequent sawtooth crash may result from the flattening of the current profile because of the locally enhanced transport of the suprathermal electrons due to the magnetic island.