One of necessary prerequisites to design cushioned package is the determination of product shock fragility, which is so far obtained by means of destructive method on shock testing machines. This paper presents a non-destructive method--power flow method to predict the product fragility. The transport package system was first divided into two subsystems to simplify analysis. The energy of critical component of the product was then calculated by applying a power flow equilibrium equation. And finally, the parameters of the transport package system, such as the input power, the internal loss factor and the coupling loss factor, were discussed.