Disclosed are a data transmission method, a network side device and a terminal. The method comprises: a terminal multiplexing a first resource to transmit first data, wherein the first data is data of a first service, the first resource is a resource in a second resource for transmitting second data, the second data is initial transmission data of a second service, and the delay requirement of the first service is higher than the delay requirement of the second service; and the terminal retransmitting third data on a third resource, wherein the third data is all or some of the second data. The embodiments of the present invention are beneficial to improving the data transmission efficiency of second data subjected to transmission (puncturing) of first data.