With the development of substation automation， not only breakers but also all switch gears can be remote controlled. The action of switch gear is restricted by five-prevention rules. In the 500 kV Hanshan substation， a remote control locking software is developed in the man-machine interface（MMI） system. The remote control locking software saves the logic of operation locking in the database at first. When controlling a device in the MMI system， the software takes out the device's logic of operation locking from the database to judge. The operation command can be sent out if the logic value is true， otherwise the operation command cannot be sent out. The successful application of remote control locking software makes it possible in the future that the hardware of MMI system can be simplified.