Because of the difficulty to actuate the large structures in low frequency region, the mechanical impedance data of the large structures at low frequency has small coherence factor and low reliability. In this paper, a finite element code is used to establish an FE model for large cabin structure, and the mechanical impedance of a submarine cabin base in the low frequency region is calculated. The numerical results are compared with those of experimental measurement and theoretical assessment. The feasibility for forecasting the mechanical impedance characteristics of the base in the low frequency region by means of the finite element method is evaluated. The disadvantage of the low reliability of the measured mechanical impedance data of the cabin base at the low frequency is improved. This method is valuable for engineering application.