The utility model relates to an electric power system on -line computation activestandby dual system, form in I district two sets of online safety and stability computational system coexist, mutually for the method of operation of activestandby, when the on -line computation is carried out to the main system and upload the index data to state's accent, be equipped with the system and carry out the on -line computation simultaneously but do not upload any numerical result procedure, taking place for a certain reason to crash, losing the dot OR can't normally calculate the time when the main system, main system stop work, automatic switch -over become to be equipped with the system and transfer to the state and upload procedure as a result, vice versa. The utility model discloses a dispatch on -line computation reliability and accuracy have been improved to freely switching of dual system, and practical prospect is very wide.