A finite element model for supercavitating underwater vehicles was developed and the dynamic stability of supercavitating double shells was investigated to obtain the instability maps for varying vehicle's velocity considering the time-dependent properties of the longitudinal loads. The computational results indicate that with the increment of the thickness of the annular plates linking between inner and outer shells or the number and dimension of the circumferential stiffeners, the frequencies corresponding to dynamic instability decline and the extension of the regions of dynamic instability is reduced lightly, while the frequencies corresponding to dynamic instability ascend and the dynamic stability is enhanced remarkably with the space between inner and outer shells decreased or the number and dimension of the longitudinal stiffeners increased.