The present study aims to examine the effect of prewriting planning on writing performance in EAP(English for Academic Purposes) course context and the moderating effect of individual differences.Adopting a 2×6 two-factor mixed experiment design, a reading-based academic writing task is conducted, in which the independent variable is prewriting condition-concept-mapping planning(by experimental group, N=202) vs.zero planning(by control group, N=196);dependent variable is writing performance;and two learner factors(English proficiency and task motivation) combine into a moderating variable with 6 levels.T test finds that the surface content richness(i.e.article length), deep content richness(i.e.critical thinking level) and lexical sophistication(i.e.ratio of academic words and offlist words) of experimental group are significantly higher than that of control group, and that there is no significant difference in lexical variety(D value of TTR).This finding indicates a positive effect of reading-based concept mapping prewriting planning on content richness and lexical sophistication in EAP writing.ANOVA analysis also finds significant main effects of both prewriting planning and individual differences(proficiency & task motivation) on writing results, but their interactive effect is limited to lexical sophistication, which suggests a very limited moderating effect of individual difference factors.In light of above findings, implication for the selection of potential students for EAP teaching is also mentioned.