The invention discloses a data transmission method and device and belongs to the technical field of terminals. The method is applied to a mobile terminal. The mobile terminal comprises an application processor AP system and a baseband processor BP system. The method comprises the steps that when the AP system is in a sleep state, data is cached whenever the BP system receives the data sent by network equipment; when at least one data which is determined to be cached by the BP system meets preset transmission conditions, the AP system is awakened, and at least one data is sent to the AP system. When the AP system is in the sleep state, data is cached at first rather immediately awakening the AP system to send the data whenever the data sent by the network equipment is received, the AP system is awakened after the at least one cached data meets the preset transmission conditions, the cached data is sent to the AP system, the AP system awakening frequency is reduced, and power consumption and electric quantity of the mobile terminal are saved.