A backrest inclination structure for lumbar support enables a backrest to enter a free state when a user sitting at any position of a chair lifts a lever of a spring continuous control unit, such that the backrest fits the user's moving back when the backrest is configured for movable inclination. Hence, the backrest can move together with the user's back ergonomically to provide lumbar support. Accordingly, the user can sit comfortably on the chair and be free from lumbago and kyphosis which are common among sedentary individuals.