Abstract: A great amount of liquid nitrogen and power is consumed to run the cryogenic wind tunnel. The temperature variation of the wind tunnel may cause excessive thermal deformation and stress, which can have a significant influence on the wind tunnel safety. Thus, it is indispensable to develop the reliable thermodynamic model of the cryogenic wind tunnel for evaluating the safety, performance and economy efficiency. In this paper the cryogenic wind tunnel diffuser is studied and its thermodynamic model is established based on the finite elements method. Moreover, the response surface method is adopted to correct some model parameters for purposes of improving the consistency between the finite elements model and the actual model. Firstly, according to the differences between the test data and simulation results the internal surface convective heat transfer coefficients of the plenum tapered shell are chosen as the parameters that need to be corrected. Secondly, the sample space of the finite elements thermal analysis is generated by using the central composite experiment design. Thirdly, the nonlinear regress analysis of the residual mean square is carried out in the sample space to establish the response surface model. Finally, the residual mean square sum of all monitor results is taken as the objective function and then the thermodynamic model is analyzed and optimized by means of the nonlinear multi-object optimization algorithm. The model verification results show that the updated thermodynamic model is highly consistent with the actual model and it is feasible to correct the thermodynamic model with the response surface method.