Abstract: The application of the difierence curvature index for the damage detection is limited because of the loading mode. In this paper, a loading mode based on the truck is proposed. The working condition of the concentrated load can be obtained after the twice truck loading. A damage detection method for bridges of simply supported beams is established by a new indicator called the truck load difierence curvature indicator (TLDCI). According to the measured vertical displacement data, a graph of the TLDCI can be established. The occurrence and the localization of the damage then can be identifled and the early warning for the bridge damage can be realized. The TLDCI method involves a simple calculation and does not require the prior information of the intact bridge. Its efiectiveness is validated by an example. Finally, how to improve the stability of this new method is discussed.