A method for determining a slot-format includes that: a terminal device receives an indication signal from a network device, the indication signal having a first association with a downlink transmission opportunity obtained by the network device; and the terminal device determines a slot format according to the indication signal. Another method for determining a slot format includes that: a network device sends an indication signal after obtaining a downlink transmission opportunity, the indication signal having a first association with the downlink transmission opportunity and the indication signal being used for a terminal device to determine a slot format. A terminal device and a network device are also provided.