In order to improve the accuracy of the decision of mountain tunnel construction site layout plan, a plan preference model based on the improved gray target decision was proposed with the example of the six construction site layout options in the Niuluan Village Tunnel. Firstly, by analyzing the influencing factors of construction site layout, the evaluation index system with feasibility, economy, environmental impact and social benefit was constructed. Secondly, using the cloud model, the qualitative indicators were quantified and the indicator weighs were determined using criteria importance though intercriteria correlation (CRITIC). Finally, based on the information value of the gray correlation difference, in combination with the calculation of the Euromed theory, the weighted target center gap was revised, the program preference was achieved through the contrast of the target center distance, and the index sensitivity analysis was carried out using the one-at-a-time (OAT) method. The results show that the scheme selected based on the improved gray target decision is consistent with the actual selection scheme, the weighted target center gap is 0.610, and the selected scheme is consistent with the actual scheme, and the "landform change" is analyzed as the index with the greatest impact on the selection of the scheme. Thus the method present the advantages and disadvantages of each scheme, which make the selection of mountain tunnel construction site layout scheme more scientific and reasonable.