Abstract: Finite size array with high array gain looks very attractive but is hard to handle in practice, especially for underwater acoustic applications. This paper proposes a calibration method for this kind of array in underwater bounded space at low-frequency range. Transient state signal is analyzed and used to minimize the reflection effect of walls. Simulation results and water tank tests show the efficiency of the use of transient state signals. A calibration method is established for entire array in underwater bounded space, with corrections of sound field distortion. Experimental data shows good agreement with theoretical prediction, thus the suggested method provides a basis for the future work.