A variable-bandwidth design method based on the principle of energy equivalence was proposed for the random vibration environmental test condition of launch vehicles. By adopting the fractional octave frequency band data processing method and keeping the RMS (root mean square) in every frequency band identical with the one of the original power spectral density, the exorbitant RMS problem of the traditional constant-bandwidth random vibration environmental test condition was avoided. To validate the capability of the method, the random vibration simulations of a typical pipeline were conducted. The results indicate that the method is able to assess the product effectively rather than excessively. The proposed variable-bandwidth design method offers an efficient alternative for the conditions design in the random-vibration environment test of launch vehicles.