In this paper, a study on the characteristics of a store in open cavity is conducted. The flows over the store in the cavity are simulated with RANS and DDES solvers. To investigate the aerodynamic characteristics of the store in the cavity, the change in the cavity flow due to the wind tunnel support are analyzed. The wind tunnel test result and both computational results are compared. SPL and FFT analysis are conducted and compared with the frequency obtained by Rossiter’s equation for quantitative comparison unsteady cavity flow. The SPL analysis results of RANS and DDES indicate that small eddies inside the cavity affect the third mode and higher frequencies. However, there is no significant difference in the two results in the time-averaged surface pressure distributions. Moreover, the FFT analysis of the aerodynamic coefficient of the store in cavity shows little differences between RANS and DDES results.