Tidal inlets represent a typical tidally dominated sedimentary environment. The entrance channel of an inlet system tends to serve as a natural navigation channel, which is important for harbours. From the viewpoint of morphodynamics, the inlet system is also important because its formation and evolution are concerned with a number of crucial dynamic processes. Under the dynamic equilibrium condition, there is a power law relationship between the cross-sectional area and tidal prism. However, the parameter n in the equation varies considerably for different regions if the O′Brien method is applied. These values do not truly represent the equilibrium condition because some inlet systems involved in the regression analysis have not reached equilibrium. The power law relationship can also be defined on the basis of a sediment dynamic approach, which generates a stable n value (around 1.15). With regard to the shape of the cross-section, small inlet systems are different from large ones. In response to the intense sediment transport and accumulation associated with small inlets, the cross-section tends to have a combined shape,i.e., a channel with a large depth to width ration scoured into the bed of a wide and shallow channel. Such a shape enhances the stability of small inlets systems and results in more complicated time-velocity asymmetry patterns. These results may be applied to small inlets in coastal development activities. Since the cross-sectional morphology is related to the entire entrance channel and the associated tidal deltas, a thorough understanding of the cross-sectional morphology depends upon further studies of the feedbacks among the hydrodynamic processes, sediment transport and accumulation and the overall morphology of the channel, the coupling of the growth of the tidal deltas and the processes of tidal basin infilling, and the techniques of quantitative simulation of the channel morphological evolution.