An over-the-air, OTA, technology data sending method, comprising: obtaining, by a first server, a new version of encrypted data and an old version of encrypted data of system software applied to a mobile terminal; removing, by the first server, signature data from the new version of encrypted data, to obtain a new version of encrypted original data; removing, by the first server, signature data from the old version of encrypted data, to obtain an old version of encrypted original data; decrypting, by the first server, the new version of encrypted original data to obtain a new version of original data, and decrypting the old version of encrypted original data to obtain an old version of original data; performing, by the first server, differentiation on the new version of original data and the old version of original data, to obtain differential data, wherein the differential data comprises data that is in the new version of original data and that is different from the old version of original data; generating, by the first server, OTA data, wherein the OTA data comprises differential encrypted data and header information, the differential encrypted data comprises differential ciphertext data obtained after the differential data is encrypted and differential signature data obtained by signing the differential ciphertext data by using a private key of the first server, the header information comprises differential data encryption header information and destination data encryption header information, the differential data encryption header information is used by the mobile terminal to decrypt the differential encrypted data to obtain the differential data, and the destination data encryption header information is used by the mobile terminal to verify the differential signature data of the differential encrypted data; and sending, by the first server, the OTA data to the mobile terminal, wherein the OTA data is used to upgrade an old version of the system software of the mobile terminal to a new version obtaining, by a first server, a new version of encrypted data and an old version of encrypted data of system software applied to a mobile terminal; removing, by the first server, signature data from the new version of encrypted data, to obtain a new version of encrypted original data; removing, by the first server, signature data from the old version of encrypted data, to obtain an old version of encrypted original data; decrypting, by the first server, the new version of encrypted original data to obtain a new version of original data, and decrypting the old version of encrypted original data to obtain an old version of original data; performing, by the first server, differentiation on the new version of original data and the old version of original data, to obtain differential data, wherein the differential data comprises data that is in the new version of original data and that is different from the old version of original data; generating, by the first server, OTA data, wherein the OTA data comprises differential encrypted data and header information, the differential encrypted data comprises differential ciphertext data obtained after the differential data is encrypted and differential signature data obtained by signing the differential ciphertext data by using a private key of the first server, the header information comprises differential data encryption header information and destination data encryption header information, the differential data encryption header information is used by the mobile terminal to decrypt the differential encrypted data to obtain the differential data, and the destination data encryption header information is used by the mobile terminal to verify the differential signature data of the differential encrypted data; and sending, by the first server, the OTA data to the mobile terminal, wherein the OTA data is used to upgrade an old version of the system software of the mobile terminal to a new version