The application provides a signal transmission method, a terminal device and a network device. In the method, transmission of a Primary Synchronization Signal (PSS) in an SS block occupies M PRBs, a ZP CSI-RS is located on N PRBs. In a case where the ZP CSI-RS is located on a symbol occupied by the SS block, the terminal device determines that at least one first RE does not include the ZP CSI-RS or determines that the at least one first RE includes the ZP CSI-RS, the at least one first RE being at least one RE, except one or more REs overlapped with the maximum-frequency PRB in the M PRBs, in a first PRB, and/or, the at least one first RE being at least one RE, except one or more REs overlapped with the minimum-frequency PRB in the M PRBs, in a second PRB