Tidal current asymmetry plays an important role in the net sediment transport and morphological evolution in the delta，and large-scale sand excavation activities in the Pearl River Delta（PRD）have caused significant descending of the riverbed in recent years，so it is important to study the spatial and temporal variation patterns of tidal current asymmetry in the PRD after riverbed descending. This paper establishes a two-dimensional hydrodynamic model which using topographic data of the PRD in 1999 and 2010 to simulate the hydrodynamic process in the Pearl River estuary network during the dry season. Using nonstationary harmonic analysis method to decompose velocity signals，the skewness method is used to quantify the contribution of tidal combinations，residual flow and interaction between tidal components and residual flow to tidal current asymmetry. The study shows that：1）Tidal current asymmetry is ebb dominant in the PRD due to the influence of the residual flow. 2）After riverbed descending，contribution of tidal combinations to tidal current asymmetry shows increasing trend，tidal current asymmetry weakens in the lower reaches and strengthens in the middle and upper reaches，and the change of the middle and upper reaches of the PRD is greater than that of the lower reaches.3）Changes in the interaction between tidal components and residual flow are the main cause of this phenomenon.