The current bid evaluation method can no longer meet the needs of green construction of railway construction projects, so a bid evaluation method based on an improved PCA-gray variable weight clustering model is proposed. A bid evaluation index system for railway green construction projects with a hierarchical structure was constructed from three aspects: basic construction ability, business ability and green construction ability, and the index evaluation criteria were given. Considering the high dimensional complexity of the bid evaluation system, the improved PCA method was used to reduce the dimension of the bid evaluation system, and on this basis, an improved linear weighted comprehensive evaluation function was constructed to preliminarily evaluate the construction ability of bidders. Then, the grey variable weight clustering model is used to construct the definite weighted function to further analyze the green construction ability of the bidders and select the optimal bidder. Finally, the method was applied to the bid evaluation of railway engineering projects from Lanzhouxi to Zhongchuan Airport, and the conclusion is consistent with the actual bidders, which proves the applicability and effectiveness of the model.