Research purposes：Design and construction of bridge are the key points to the modern railway construction. It is difficult to design and construct the bridge in karst area because of the development of underlying karst under the bridge site, complex shapes of karst on the base and lots of karst carves. These maybe cause the stratum collapse, sudden change of rock surface and leakage of karst carve in course of construction of the bridge foundation. Based on the design and construction of one railway bridge in karst area, this paper sums up the experiences in design of the bridge foundation in karst area and its construction technologies and makes some proposal.