Writing in English might be one of the most difficult tasks for EFL (English as a Foreign Language) learners. This paper presents FLOW, a writing assistance system. It is built based on first-language-oriented input function and context sensitive approach, aiming at providing immediate and appropriate suggestions including translations, paraphrases, and n-grams during composing and revising processes. FLOW is expected to help EFL writers achieve their writing flow without being interrupted by their insufficient lexical knowledge.