Abstract-Using the resources in Appraisal theory (Martin & White, 2005), this paper contrastively examines a total of 124 Chinese undergraduate EFL argumentative essays in two dimensions: how two different essays topics initiate different evaluative patterns in EFL and L1 essays; what distinguishes EFL from L1 writers' evaluative language in argumentative essays. The corpus-based study reveals that though native and non-native writers display similar appraisal pattern in dealing with different essay topics, native speakers use more negative evaluative language to bring out potential contradictory points. The study suggests that EFL learners' deficiency in lexical proficiency, especially of those expressing negative and polarizing meanings may hinder their capacity in critical thinking involved in argumentative writing tasks. With effective teaching strategies, the enhancement of the lexical proficiency of evaluative language can boost EFL students' persuasive writing ability and their overall writing capacity.