A method performed by the transmitting end of a terminal for data transmission, comprising: compressing, for a data packet with a TCP/IP header, the TCP/IP header by a Packet Data Adaptation Protocol PDAP layer or a Packet Data Convergence Protocol PDCP layer to obtain a data packet with the compressed TCP/IP header; and adding a PDCP header into the data packet with the compressed TCP/IP header and transmitting a data packet with the compressed TCP/IP header and the PDCP header to a lower layer, characterized by that the compressing, for the data packet with the TCP/IP header, the TCP/IP header by the PDCP layer to obtain the data packet with the compressed TCP/IP header comprises: adding, by the PDAP layer, a PDAP header into a head of the data packet with the TCP/IP header, and adding indication information for indicating a length of the PDAP header into a data packet that is added with the PDAP header, to obtain the data packet with the PDAP header; and transmitting the data packet that is added with the PDAP header to the PDCP layer; and removing, by an entity at the PDCP layer other than a compression entity, the PDAP header from the data packet, and performing, by the compression entity at the PDCP layer, a header compression on the data packet except the PDAP header, or wherein the compressing, for the data packet with the TCP/IP header, the TCP/IP header by the PDAP layer to obtain the data packet with the compressed TCP/IP header comprises: compressing, by a compression entity configured by the PDAP layer, the TCP/IP header of the data packet, and adding a PDAP header into the compressed data packet, to obtain the data packet with the compressed TCP/IP header. compressing, for a data packet with a TCP/IP header, the TCP/IP header by a Packet Data Adaptation Protocol PDAP layer or a Packet Data Convergence Protocol PDCP layer to obtain a data packet with the compressed TCP/IP header; and adding a PDCP header into the data packet with the compressed TCP/IP header and transmitting a data packet with the compressed TCP/IP header and the PDCP header to a lower layer, characterized by that the compressing, for the data packet with the TCP/IP header, the TCP/IP header by the PDCP layer to obtain the data packet with the compressed TCP/IP header comprises: adding, by the PDAP layer, a PDAP header into a head of the data packet with the TCP/IP header, and adding indication information for indicating a length of the PDAP header into a data packet that is added with the PDAP header, to obtain the data packet with the PDAP header; and transmitting the data packet that is added with the PDAP header to the PDCP layer; and removing, by an entity at the PDCP layer other than a compression entity, the PDAP header from the data packet, and performing, by the compression entity at the PDCP layer, a header compression on the data packet except the PDAP header, or wherein the compressing, for the data packet with the TCP/IP header, the TCP/IP header by the PDAP layer to obtain the data packet with the compressed TCP/IP header comprises: compressing, by a compression entity configured by the PDAP layer, the TCP/IP header of the data packet, and adding a PDAP header into the compressed data packet, to obtain the data packet with the compressed TCP/IP header. adding, by the PDAP layer, a PDAP header into a head of the data packet with the TCP/IP header, and adding indication information for indicating a length of the PDAP header into a data packet that is added with the PDAP header, to obtain the data packet with the PDAP header; and transmitting the data packet that is added with the PDAP header to the PDCP layer; and removing, by an entity at the PDCP layer other than a compression entity, the PDAP header from the data packet, and performing, by the compression entity at the PDCP layer, a header compression on the data packet except the PDAP header, or wherein the compressing, for the data packet with the TCP/IP header, the TCP/IP header by the PDAP layer to obtain the data packet with the compressed TCP/IP header comprises: compressing, by a compression entity configured by the PDAP layer, the TCP/IP header of the data packet, and adding a PDAP header into the compressed data packet, to obtain the data packet with the compressed TCP/IP header.