Abstract: The key to realize soft start of multiple oil pumps by using one frequency converter is two way switch over between reverse converter and operating frequency power. In order to counter the harmful problems to power networks caused by unstable equipment operation and surge current in the secondary startup of the mo tor, surge-free switch over must be realized, which requires a conformation between the frequency, phase and amplitude output from reverse converter and that in operating frequency power network. To realize surge-free switch over, developed are a change over switch and the distribution circuits and the multiswitch controlled circuits, which are suitable for multipump startup. It is proved by over one year applications by users that the prototype has met all the design requirements, and has guaranteed, without failure, fuel filling to the airplanes as well as loading, unloading and transfer operation in tank farm.