## 1 Introduction  
At present, China's construction productivity is growing and tremendous investments are made in the construction industry. However, the development of China's infrastructure is unbalanced in different regions. Meanwhile, achieving sustainability becomes an essential objective for the construction industry. Especially, construction project practice is facing a series of challenges in such regions where the environment is degraded beyond the level that can maintain the current human use and development for a long time under the current socio-economic and technological level [1, 2]. These particular regions are defined as Ecologically Fragile Regions (EFRs) [3, 4] in this study. For instance, the lack of water resources and the vulnerability of the natural geographical environment are two important ecologically fragile factors in the arid regions of China [5, 6]. This means that construction activities taking place in EFRs are facing a series of environmental obstacles, includingsaline soil [7], reduction of groundwater, drying surface water, land salinization and the sharp decline in plant and biological species [8; 9; 10; 11]. These barriers may bring difficulties for the construction project conducted in EFRs, have negative impacts on the performance of the construction project and even result in their failure [12; 13]. Hence, studying the effective ways to arrive at project success is needed and is crucial for the benefit of the project managers and participants who undertake construction projects in EFRs. Construction activities are a result of the combination of a set of schemed projects or events and their outputs with different stakeholders and participants in the whole life cycle. Among the series of events, the particular ones which have the most critical influence on achieving a successful construction project are defined as critical success factors (CSFs) [14; 15; 16; 17; 18]. CSFs which have a risk management nature [19] is initially proposed by [PERSON] [20] as the group of special events that contribute to project success. Thereafter, a large body of studies [21; 22; 23; 24; 25; 26; 27; 28; 29] have investigated CSFs for construction projects. These prior studies have provided some new perspectives for the scholars in the research field of project management and participants involved in construction project practice to allocate the limited resources of a project to a certain number of factors [30; 31] which promote construction project success by the process of investigation and identification of CSFs. Although the significance of studying CSFs in construction projects was gained, emphasized and strengthened, prior studies are mainly focused on the construction project conducted in non-EFRs. However, CSFs are special for various construction projects under changeable scenarios, such as the external environment, the different delivery methods of projects and project types etc. [32; 33] The consensus is that there is a lack among researchers regarding the CSFs for a construction project in EFRs. Hence, exploring the CSFs for a construction project in EFRs is meaningful and necessary and there is a great potential for exploring the interrelationships between CSFs. The present study aims to systematically identify CSFs for a construction project in EFRs, and focuses on structuring the CSFs using a hierarchal model. The objectives are: (1) identifying the CSFs through a literature review from a multi-perspective and a particular construction project; (2) investigating the interrelationships between CSFs and obtaining relevant direct factors, indirect factors, and root factors; and (3) developing a clear structure for a hierarchy model of the CSFs, and establishing a hierarchical order to prioritize them using ISM (Interpentive Structural Modeling).