A blade structure for centrifugal fan includes a hub, a first blade unit, and a second blade unit. The hub includes at least one connection section, to a radially outer end of which an annular body is connected. The annular body has a first side and an opposite second side; and the first and the second blade unit are arranged on and spaced along the first and the second side of the annular body, respectively. By providing the first and the second blade unit around the hub of a centrifugal fan, the air flows and pressure produced by the centrifugal fan can be largely increased at effectively reduced noise.