Designed highest navigable water level has a direct impact on bridge reconstruction scheme.Based on the difficult situation of bridge reconstruction for inland channel in plain river network,we carry out some research on bridge reconstruction cases,characteristic of typical water level curve,current navigation situation of ship going through the bridge,bridge strike accidents,the development of navigation aids and management means in inland waterways,etc.We discuss the possibility of reducing the designed highest navigable water level,and propose a scheme which regards navigable guarantee rate as the base of the designed highest navigable water level,and the scheme is supplemented by a perfect traffic management system.This scheme can be used as a reference to the designed highest navigable water level in the plain river network area,which has a perfect navigation aids system and a high management level.