From the point of language universals and language acquisition，this paper attempts to
find why some segments or some rules which describe phonological phenomena are more
natual than others. The more the description of human language reflects the naturalness of language the better it is. In this paper the naturalness of phonology is discussed from the point of view both of SPE theory and Stampe's natural phonology，
and it is concluded that the natualness of language and language acquisition are not so fully described by the SPE markedness theory as by Stampe's natual phonology， which makes a distinction between phonological processes and acquired phonological rules.