Risk assessment that usually is applied to identify, control and reduce the hazardous consequences, is a main stage of risk management and for dings it, different methods has been illustrated. In the studied of this area, most of those, are categorized risk assessment approaches into two approaches; deterministic and probabilistic with qualitative, quantitative and mixed (semi- quantitative) and are introduced each of the following methods. The studies show, there is not a single way, that is acceptable, to put a method in different group. Obviously, this issue will lead to ambiguity and confusion of risk assessors in finding optimal method. Investigating of this issue and finding an acceptable answer is the main purpose of this article.In this paper, different criteria for selecting risk assessment methods have been introduced and explained. These criteria include the purpose of risk assessment in studied area, data collection methods, variable measuring scales, and finally, data analysis. Based on new criteria, the comprehensive algorithm for categorizing these methods presented. Examples of various risk assessment methods and their applications have been addressed