A method for transmitting data, an access network device and a terminal device are provided. The method includes the following steps: an access network device receives a first data packet sent by a core network device, and determines a state that the terminal device needs to be in for receiving the first data packet, the state that the terminal device needs to be in for receiving the first data packet is any of at least two states, and the at least two states are different states when the terminal device is in data transmission with a network side device; the access network device sends the data packet to the terminal device.