An upgrade method for a vehicle-mounted device, applied to a vehicle-mounted system, wherein the vehicle-mounted system comprises a vehicle-mounted control device and one or more to-be-upgraded vehicle-mounted devices, and the method comprises: obtaining, by the vehicle-mounted control device, a vehicle-mounted upgrade package, wherein the vehicle-mounted upgrade package comprises a plurality of upgrade files, and each upgrade file is used to upgrade at least one to-be-upgraded vehicle-mounted device; performing, by the vehicle-mounted control device, security verification on the plurality of upgrade files; and sending, by the vehicle-mounted control device, a target upgrade file to a target to-be-upgraded vehicle-mounted device that is to be upgraded by using the target upgrade file, wherein the target upgrade file is an upgrade file on which security verification succeeds in the plurality of upgrade files, wherein the sending, by the vehicle-mounted control device, a target upgrade file to a target to-be-upgraded vehicle-mounted device that is to be upgraded by using the target upgrade file is characterized by dividing, by the vehicle-mounted control device, the target upgrade file into a plurality of upgrade subfiles; generating, by the vehicle-mounted control device, a plurality of mutually associated data blocks from the plurality of upgrade subfiles by using a preset algorithm, and generating a first message authentication code MAC of the plurality of data blocks by using a second key, wherein the second key is a symmetric algorithm key; and sequentially sending, by the vehicle-mounted control device to the target to-be-upgraded vehicle-mounted device, the plurality of data blocks that carry the first MAC. obtaining, by the vehicle-mounted control device, a vehicle-mounted upgrade package, wherein the vehicle-mounted upgrade package comprises a plurality of upgrade files, and each upgrade file is used to upgrade at least one to-be-upgraded vehicle-mounted device; performing, by the vehicle-mounted control device, security verification on the plurality of upgrade files; and sending, by the vehicle-mounted control device, a target upgrade file to a target to-be-upgraded vehicle-mounted device that is to be upgraded by using the target upgrade file, wherein the target upgrade file is an upgrade file on which security verification succeeds in the plurality of upgrade files, wherein the sending, by the vehicle-mounted control device, a target upgrade file to a target to-be-upgraded vehicle-mounted device that is to be upgraded by using the target upgrade file is characterized by dividing, by the vehicle-mounted control device, the target upgrade file into a plurality of upgrade subfiles; generating, by the vehicle-mounted control device, a plurality of mutually associated data blocks from the plurality of upgrade subfiles by using a preset algorithm, and generating a first message authentication code MAC of the plurality of data blocks by using a second key, wherein the second key is a symmetric algorithm key; and sequentially sending, by the vehicle-mounted control device to the target to-be-upgraded vehicle-mounted device, the plurality of data blocks that carry the first MAC. dividing, by the vehicle-mounted control device, the target upgrade file into a plurality of upgrade subfiles; generating, by the vehicle-mounted control device, a plurality of mutually associated data blocks from the plurality of upgrade subfiles by using a preset algorithm, and generating a first message authentication code MAC of the plurality of data blocks by using a second key, wherein the second key is a symmetric algorithm key; and sequentially sending, by the vehicle-mounted control device to the target to-be-upgraded vehicle-mounted device, the plurality of data blocks that carry the first MAC.