The single-bubble sonoluminescence spectra of the terbium chloride aqueous solutions dissolved with the noble gas Ar are studied in this paper. Under the condition of fixed driving ultrasonic frequency and different sound pressures, a series of line spectra is identified as emissions from the transitions of OH radical vibrational levels from the first excited state A2∑+ to the ground state X2Π, including (0, 0) transition at 307 nm, (0, 1) transition at 335 nm and (1, 0) transition at 276 nm and so on. The experimental results show that higher sound pressure is conducive to the appearance of the line spectrum at 276 nm while lower sound pressure is favorable for the appearance of the line spectra at 307 nm and 335 nm. The relative intensity of the line spectrum in the total spectrum is expressed quantificationally by defining an intensity ratio of the line spectrum to the continuous spectrum. In addition, the effects of the driving sound pressure on the intensity ratios of different line spectra are given.