Abstract: A composite cable-pylon with a steel-anchor-box as a new developed structure was adopted in long-span cable-stayed bridges recently. Bearing the inclined cable force, the composite pylon burdened not only vertical forces but horizontal forces in a horizontal plane which usually is the key mechanical issue controlling the structural design. Studying the configuration and mechanical behavior of a composite cable-pylon with a steel-anchor-box, a simplified analytical model for the horizontal mechanical behavior of a composite pylon is proposed. Comparing to finished experimental results, the rationality and accuracy of this simplified analytical model are verified.