Abstract: In this paper, by use of the normal-mode method, the sound field of the turning-point convergence-zones in underwater sound channel is treated.Theoretical analysis shows that the sound field of the turning-point convergence-zone is the superposition of a great number of in-phase normal modes.Under certain conditions, the sound intensity at the turning-point convergence-zone is proportional to r^-2, the convergence-gain is independent to the order of zone and the width of zone is proportional to the order of zone. These theoretieal results are consistent with Hale 's experiment.