The invention provides an earthing switch locking device, an earthing switch, and a combined switch. The earthing switch comprises an earthing switch interlocking plate which is disposed on a rotating shaft of the earthing switch. The earthing switch interlocking plate is provided with a blocking end, and is also provided with an adjustment part. The adjustment part is provided with an extension segment which extends forwards from the blocking end and is used for abutting against a disconnecting switch interlocking plate when the earthing switch is located at a switching-off position. The length of a part, extending out of the blocking end, of the extension segment can be adjusted. In use, the extension segment of the adjustment part abuts against the disconnecting switch interlocking plate. The earthing switch can achieve the effective locking, is prevented from rotating in the switching-on direction, and is relatively reliable in locking.