Provided are a method and an apparatus for transmitting uplink data in a wireless communication system. Specifically, a first terminal transmits a random access preamble for requesting a connectionless transmission. The first terminal receives a random access response comprising scheduling information of the uplink data. The first terminal transmits uplink data and a reference signal from a first resource configured on the basis of scheduling information of the uplink data and information indicating the CP length of the reference signal. The CP length of the reference signal can be configured to be identical to the CP length of the random access preamble. The first resource can correspond to a resource utilized by both the first terminal and second terminal.