Disclosed are a spectrum allocation method and device for an optical network and a computer storage medium. The method comprises: segmenting a service path of an optical network to obtain at least one path segment; trying to allocate, in sequence, for each path segment of the service path a service processing manner that satisfies a service spectrum requirement; and when the service processing manner satisfies the service spectrum requirement, allocating a frequency used by each path segment on the service path according to the currently allocated service processing manner of each path segment of the service path.