A method and a device for transmitting an uplink transmission block in a wireless communication system are provided. Particularly, a terminal receives, from a base station, allocation information on a first grant-free uplink resource, which is scheduled semi-persistently. The terminal repeatedly transmits a first transmission block through the first grant-free uplink resource by using a first reference signal. The terminal transmits a second transmission block by using a second reference signal before completion of the transmission of the first transmission block. The second transmission block is distinguished from the first transmission block through a change of the first reference signal to the second reference signal.