Examples of a data transmission method and apparatus in TEE systems are described. One example of the method includes: obtaining first data; obtaining a write offset address by reading a first address; obtaining a read offset address by reading a second address; determining whether the number of bytes in the first data is less than or equal to the number of writable bytes, where the number of writable bytes is determined based on the write offset address and the read offset address, and each address corresponds to one byte; when the number of bytes in the first data is less than or equal to the number of writable bytes, writing the first data into third addresses starting from the write offset address; and updating the write offset address in the first address.