There is a lack of limit power calculation method for the correlative transmission interfaces， and the high computational cost associated with enumerating combination makes it unsuitable for online applications. A fractional step calculation strategy is proposed based on the distributed parallel processing technology. This strategy firstly calculates the static limit power and then calculates the transient and dynamic limit power. A searching strategy of security check in parallel and iteration is proposed as well. The proposed strategy can be used to select the evaluated fault set of next limit power calculation and improve the searching speed of limit power. It can also be used to calculate the interacted influence factors of correlative transmission interface limit power， so as to provide the decision support for dispatching operation control. Case studies of China Southern Power Grid prove the rapidity and effectiveness of the proposed method.