Safety is very important aspects of construction projects which are the most hazardous endeavors have many work-related injuries and accidents. Accordingly, safety factors must be considered in project lifecycle from beginning of a project to its end. To improve project safety, the definition of safety factors and determination of their importance are necessary. In some of the previous researches several safety factors are introduced. In this paper, safety factors in construction project are reviewed and categorized as well as an exhaustive classified catalogue of critical safety factors in construction project which don't have unnecessary details is developed. The identification of the critical safety factors which are categorized in four main groups consists of safety approach, safety engineering, safety management and safety on construction site will enable appropriate allocation of limited resources.