Embodiments of the present invention provide a method for transmitting physical layer data and a data transmission device, which can reduce limitations of limited transmission bandwidth resources to transmission of physical layer data in a base station. The method comprises: determining a target bit width of physical layer data, the target bit width being N bits; determining to-be-transmitted data the bit width of which is N bits, values of all or some of bits in the to-be-transmitted data being values intercepted sequentially starting from a highest non-zero bit of the physical layer data to lower bits; and sending the to-be-transmitted data to a peer end. In the embodiments of the present invention, by performing bit width conversion of physical layer data and reducing a data rate, limitations of limited transmission bandwidth resources to transmission of physical layer data in a base station can be effectively reduced, thereby improving the data transmission efficiency and improving the user experience.