The Chinese idiom 火上浇油 is formed by directly combining the characters 火 (fire), 上 (on), 浇 (pour), and 油 (oil) in sequence, creating a literal phrase meaning "to pour oil on fire". Each character contributes its basic meaning to construct a vivid image of an action that intensifies a base element, with the entire composition serving as a fixed expression where the literal components convey the core concept.