The total stiffness of a three-pylon suspension bridge is relatively small. The middle pylon structure of a three-pylon suspension bridge has great influence on the mechanical behavior of the whole bridge. The contradiction between the slip factor of main cable on the top of pylon and the ratios of the deflection to span of the bridge needs to be solved. Based on the analysis of the characteristics and structural behavior of middle pylon of Taizhou Bridge, structure selection of the pylon is done and longitudinal herringbone steel pylon is taken. The structure design of steel pylon and process with key structures, which include weld design for thick plates, structure dispose of branching nodes, connection type between the bottom of steel pylon and concrete bearing platform are introduced. The longitudinal blocking partition design based on crane capacity is also introduced.