The thermo-hydraulic analysis of reactors is an important technical support for the safety analysis and evaluation of nuclear power plants. Currently, using software to carry out simulation modeling and doing partial experimental verification has already become an important means of scientific research and engineering training. CosCONT software is a containment thermal response analysis module in the core physics-thermal design and system safety analysis software package (COSINE) developed by the Institute of Nuclear Energy and Nuclear Technology of the State Power Investment Corporation of China, and cosCONT can be used to simulate various thermodynamic conditions in the reactor containment. In the process of computer simulation modeling, the settings and input parameters will bring a certain uncertainty. Therefore, it is necessary to make an uncertainty analysis of the software simulation results. Due to the pressure changes in containment under the accident conditions, the nuclear power plants will produce some failure behavior, so in this paper, we based on the cosCONT software, making some simulations of the specific accident conditions in the operation of a nuclear power plant, and choosing containment pressure change as results, compared with the experimental pressure results of a lab bench, calculating the deviation between the two, through error analysis, normality test and other methods to make uncertainty quantification. We can obtain the uncertainty distribution of the pressure, so we can evaluate the reliability of cosCONT against containment pressure, and analyze the critical influencing factors to provide any relevant recommendations for the appropriate use of the software.