Because of the influence of tide reserving,the widening rate of the tidal estuarine regulation line should be taken into consideration in the tidal estuary renovation project.There are many empirical formulae for calculating the widening rate,of which the tidal range and tide reserving coefficient are two key parameters,therefore the reasonable value of these parameters is critical.The theoretical analysis based on the basic formula derived from the widening rate formula shows that its more reasonable if the tide range value is set as the water-level difference during ebb process;as far as the renovation projects tide reserving coefficient is concerned,it is too simple to take 1.0 and 0.5 respectively in the high and moderate tidal levels proposed by the existing literature.We analyze the renovation project of the Guanhe Estuary and the north channel of the Yangtze Estuary,and the results show that the renovation projects tide reserving coefficient is not only related to the building altitude that is to be regulated,but also closely related to the layout of the renovation project.In some cases,the coefficient can be calculated by the empirical formula presented in this paper.Under complicated circumstances,the value of the coefficient is suggested to be determined in combination with the mathematical model or physical model.