A method, an apparatus and a system for data transmission are provided. The method includes: receiving processed first microwave data information that is received through a microwave antenna; performing multiplexing through a preset rule on the first microwave data information and processed first radio frequency data information that is received through a base station antenna, and sending multiplexed information to a baseband unit, so that the baseband unit sends the first microwave data information to a microwave indoor unit. In the method, the apparatus and the system for data transmission, microwave data information and radio frequency data information are multiplexed, and then multiplexed information is transmitted together. The microwave data information can be transmitted through a transmission medium between base station devices, such as a fiber, thereby saving connection cables between microwave transmission devices and reducing a device cost and an installation cost of the microwave transmission devices.