In this paper, the basic theory of factor analysis and the possibility of its application in the risk analysis of bridge construction was discussed. By making risk questionnaires, the basic data on the factor of bridge construction was summarized. On the basis of statistical processing of the data by SPSS 10.0 software, seven categories of main risk factors were pointed out , which are economy risk, contract and law risk , design risk, construction technique risk ,environment risk ,staff risk and material and equipment risk. Besides, the importance index and the correlation of the risk factors were calculated out. Sequentially, the risk of bridge construction can be evaluated quantitatively.