A New cost estimation method based on Monte-Carlo simulation and market investigation is proposed to consider both the uncertainties of cost estimation and their market drivers.There are several critical items exerting large impacts on the cost estimation,and they will be selected by sensitivity analysis of Monte-Carlo simulation.Then important critical items will be chosen from critical items based on methods of Likert Scale,Relative Important Indices(RII)and Normalized Important Indices(NII),as well as discipline and procurement experts experience.And they will be re-enquired in details in the market.Eventually,the re-rankings of market drivers will be acted as guidelines for carrying out project cost re-simulation,with inquired information of important critical items with more efficiency.As one case,a petrochemical Engineering Procurement Construction(EPC)contracting project in Saudi is illustrated to verify the validity and practicability of the proposed method.