The invention discloses a gear-locking device which is used for an aircraft deicing vehicle with a large arm. The gear-locking device is characterized by comprising a first approach switch, a second approach switch, a gear-locking rod and a gear lock, wherein the first approach switch is arranged on a support below the large arm of the deicing vehicle and used for detecting whether the large arm is lifted; the second approach switch is arranged close to a gear-shifting rod of the deicing vehicle and used for detecting the gear of the gear-shifting rod; the gear-locking rod is arranged over against a hole which is arranged on a gear-shifting frame of the deicing vehicle and used for limiting the gear of the gear-shifting rod; and the gear lock is slipperily connected with the gear-locking rod and electrically connected with the first approach switch and the second approach switch, and when the first approach switch detects that the large arm is lifted and the second approach switch detects that the gear-shifting rod is located in a preset gear, the gear lock controls the gear-locking rod to move to the hole on the gear-shifting frame of the deicing vehicle, thereby limiting the gear of the gear-shifting rod.