Abstract: In order to solve the problem of source depth discrimination in shallow water waveguide,a method using phase relation is proposed.In this method,the signal received from a Vertical Line Array (VLA) is used to get normal mode coefficients by mode filtering processing.In the precondition that the source distance is known,the phase relation can be obtained from the adjacent normal mode coefficients,and the depth region is discriminated based on phase relation.This method can discriminate the source depth when the number of array elements is less.It is suitable for broadband signal,narrowband signal,continuous signal and pulse signal.The analysis and the results of numerical simulation show that only the surface source can excite normal modes which are in-phase.This peculiarity can be used for surface and submerged sources discrimination.Simulation and experimental results show that this method can discriminate source depth accurately with constant or slowly varying sound speed profile.And even the depth sampling is insufficient or the mode filtering result is not ideal,it can still work.