This paper aims to make a contrastive corpus-based analysis of modal verbs used by Chinese college students in their oral and written English.The result shows:(1) Chinese college students tend to use key modal verbs,not well master the modal meaning of peripheral modals and semi-modals;(2) Chinese college students overuse some assertive modals,such as can,must,should in oral production,while in written language,assertive modals like can,should are overused,but euphuistical modals like may,could,would used well;(3) Chinese college students use more key modal verbs in oral language than that in written;(4) Chinese college students are not skilled at the using of peripheral modals and semi-modals like dare,need,used to,be supposed to,only relying on the overuse of semi-modals have to.