Are you talking about Linolium or Sheet vinyl flooring? You can put sheet vinyl over sheet vinyl, provided the underlayment is sound, the flooring is solid to it, no air pockets or lifting. Trowel a cement based floor leveler over the vinyl and then glue down your new floor.
Another method is to overlay the floor with 1/4" underlayment(particle board,strawboard or osb), nailed every 8" with ring shank nails, use a floor leveler on the seams and nails and glue down your new flooring. You can do this if the vinyl is torn and the underlayment is sound.
If for any reason there has been water damage (swelled Particleboard), or there is mold or an odor, Rip up the underlayment and replace it.