A method of source depth estimation based on the multi-path time delay difference is proposed.When the minimum time arrivals in all receiver depths are snapped to a certain time on time delay-depth plane,time delay arrivals of surface-bottom reflection and bottom-surface reflection intersect at the source depth.Two hydrophones deployed vertically with a certain interval are required at least.If the receiver depths are known,the pair of time delays can be used to estimate the source depth.With the proposed method the source depth can be estimated successfully in a moderate range in the deep ocean without complicated matched-field calculations in the simulations and experiments. A method of source depth estimation based on the multi-path time delay difference is proposed. When the minimum time arrivals in all receiver depths are snapped to a certain time on time delay-depth plane, time delay arrivals of surface-bottom reflection and bottom -surface reflection intersect at the source depth.Two hydrophones deployed vertically with a certain interval are required at least.If the receiver depths are known, the pair of time delays can be used to estimate the source depth .With the proposed method the source depth can be estimated successfully in a moderate range in the deep ocean without complicated matched-field calculations in the simulations and experiments.