The invention discloses an AC/DC large power grid coordinative optimization automatic control method. The method comprises the following steps: judging whether a stable fracture surface is out of limit according to the real-time operation manner of the power grid; starting coordinative optimization automatic control analysis and providing a plan modification decision for manual modification and confirmation; after security checking is passed, automatically sending the decision to the interested parties in a network manner; if the security checking is not passed, re-modifying or selecting a new adjusting scheme; after the interested parties receive the plan adjusting scheme, correspondingly adjusting according to the scheme; and monitoring the adjusting process until the out-of-limit is eliminated or the adjusting process is manually terminated. The invention furthermore discloses an AC/DC large power grid coordinative optimization automatic control system.