Abstract: In order to meet the needs of investment decision-making in the construction and development of China's oil and gas pipeline network in the future, it is urgent to develop a quantitative assessment method for the investment risk of long-distance gas pipeline projects, which can provide an assessment basis for investment decision-making. Herein, the investment risk assessment process of the Monte Carlo method was proposed, and a benefit model under the pipeline transportation price check mode was constructed according to the technical and economic characteristics of the long-distance gas pipeline projects. Thereby, risk assessment was performed based on a large long-distance gas pipeline project, an identification list of project investment risk factors was established through the expert scoring method, and the risk factors and grade division were quantified. Additionally, the design transportation capacity, pipeline transportation price and construction investment were clarified as the input variables by considering the triangular distribution function as the probability distribution function, and simulation calculation was conducted by the risk assessment software @RISK. The calculation results show that the financial net present value as an output variable presents some statistical law and tends to a normal distribution. The probability of the financial net present value greater than or equal to 0 is 94.4%, which indicates that the project has good profit expectations and a relatively high risk resistance capability. Moreover, the simulation calculation results verify the feasibility and effectiveness of the quantitative assessment based on the Monte Carlo method. Generally, the research results can provide a reference for the quantitative assessment of investment risks of the long-distance oil and gas pipeliness.