The invention relates to a safety belt height adjusting device, a safety belt height adjusting method, a seat and a vehicle. The safety belt height adjusting device comprises a fixed part, a movable part and a locking structure, the fixed part is used for being installed on a seat backrest, the movable part is movably connected to the fixed part in the first direction so as to be used for adjusting the height position of a safety belt from a leading-out point of the seat backrest, the locking structure is used for locking the movable part on the fixed part in the first direction, the locking structure comprises a locking piece and an electromagnet, and the locking piece locks or unlocks the movable part by controlling the power-on and power-off of the electromagnet. According to the safety belt height adjusting device, the safety belt can be led out from different height positions of the seat backrest, the tension requirements of passengers with different heights and body types for tying the safety belt are met, the body is prevented from being tightened by the safety belt, and the riding comfort can be improved.