Abstract: Affixation is the most important wordformation in Medical English，which is an efficient and meaningful tool medical students should learn to use.The results based on the empirical study show that the sequence followed by medical students in acquiring affix knowledge can be roughly described as：receptive suffix—receptive prefix—productive suffix—productive prefix.Tendency of their affix acquisition is that：there is a progressive and significant development of receptive affixes and prefix knowledge，which show more rapid progress than productive affixes and suffix knowledge.Productive affixes and suffix knowledge also develop nonsignificantly.