Abstract: The present invention discloses a method improving the sensitivity of competitive immunoassay, mainly, the small molecular substances for detection first react with the antibody/receptor sufficiently, then react with the second molecules, which locates on the solid phase and participates the competitive reactions, in a short time, which may greatly improve the sensitivity of competitive immunoassay. The present invention owns an easy operation method and a low cost, does not require expensive equipments or professional technological personnel, also, it owns a high sensitivity and adapts to a plurality of immunoassay methods.