The invention discloses a system for offshore oil field online profile control and displacement. The system comprises a water injection pipeline and a profile control and displacement pipeline with the tail end connected with a well shaft. An emulsion breaker with the inlet end connected with the water injection pipeline and the outlet end connected with the profile control and displacement pipeline is arranged between the water injection pipeline and the profile control and displacement pipeline, wherein the emulsion breaker is used for forming a profile control and displacement system. The emulsion breaker is connected with a static mixer arranged on the profile control and displacement system and close to a well mouth. The front side and the rear side of the emulsion breaker are each connected with an injection system through an opening, wherein the injection systems are used for containing agents and pumping the agents into the emulsion breaker. The problems that a large profile control and displacement device is large in occupied area and other simultaneous work is influenced are solved; the offshore platform heterogeneous online profile control and displacement construction process is achieved, and the continuous real-time profile control and displacement construction requirements are met.