Abstract: Using a "three parameter" bottom loss model, the expression for normalized vertical coherence of sound field in shallow water homogeneous layer was derived. A method was suggested, from which boundary losses at low frequencies and low grazing angles may be obtained for extensive area. From the measurement results, we obtained boundary losses for the frequency band of 0.4-3.15 kHz and grazing angle range of 0.7-15° On the basis of the results of the present work and the information in references^9,10, the frequency dependence of the transition ranges of the average sound field in shallow water can be explained satisfactorily.