The effects of computer and paper test media on EFL test-takers with different computer familiarity in writing scores and in the cognitive writing process have been comprehensively explored from the learners' aspect as well as on the basis of related theories and practice. The results indicate significant differences in test scores among the test-takers who are less familiar with computers, showing that the computer test medium has greatly impacted this group of test-takers' writing scores. From the perspective of the cognitive process, they are not significantly different in such stages as "goal-setting", "generating ideas" and "reviewing", while their "organising ideas" and "translating" stages were greatly different, owing mainly to the nature of the test medium itself.