Abstract: The construction environment of subway station is complicated with many risk sources. Great losses will be resulted in if an accident occurs. Therefore, it is very important to carry out the risk assessment in advance to reduce the risks and losses. In this paper, a three-level hierarchical structural risk index system is established based on a subway station project case, and the weight of each risk factor is assigned according to the risk occurrence probability level and risk loss level. As a multivariate statistical method, the principal component analysis method is used to build a mathematical model for principal component analysis by a matrix of linear transformation, then obtain a few potential observable comprehensive indexes (principal components) by matrix operation and finally construct comprehensive evaluation function by comprehensive indexes and the corresponding variance contribution rates, so as to calculate the comprehensive score of each risk category and reflect the magnitude of a risk by the score. As shown in the case evaluation results, the surrounding environment risks are greater than those of foundation pit and retaining structure construction, which basically reflects the actual conditions of the construction site,thus showing strong practicability of the proposed method.