Lagoon-tidal inlet system is a complex feedback sysetm. Any changes of some parameters can make a series response of the whole system. This paper emphases on the relationships be tween the parameters of the system during the morphological changes of the system. As the development of the flood tidal delta, the tidal entrance enlengthed and the lagoon areas decreased, resueting in reduction of the tide prism, and therefore?the lagoon-tidal inlet system is to be destroyed. Yuehu Lake is a semi-closed lagoon. Its evolution is speeded up by such artificial activities, as the dike in the tidal entrance and two prawn-ponds. Series effects on the stable of the lagoon-tidal inlet system caused by the dike and prawn-ponds are concerned. in order to keep the system, stable, artificial work to enlarge the remaining base of dike is needed.