The present disclosure discloses a data transmission method, device, and system, and belongs to the field of communications technologies. The method includes: receiving a data packet sent by user equipment, where the data packet carries indication information used to instruct a base station to establish a specified data connection to the user equipment; generating a first key of the user equipment based on the indication information and a public key of the base station; and performing data transmission with the user equipment based on the first key of the user equipment. According to the data transmission method, the transmitted data can be encrypted and decrypted when there is no radio resource control connection between the base station and the user equipment, thereby improving data transmission security while ensuring data transmission efficiency.