Abstract: A novel research method to study density wave oscillation of vapor-water two-phase flow using wavelet packets was applied. The eigenvalues of the density wave oscillation of vapor-water two-phase flow were picked-up by wavelet packets employing the (cha)racters of signal precision decomposition. The distribution and variation of the energy of the oscillation were observed inside the different fields of the oscillation frequency. This method will open a new angle for studying the density wave type oscillation of (vapor)-water two-phase flow.