This invention relates to a method and a system for carrying out non-loss switch in a radio access technology including: buffer-storing the down data messages sent to MSS at source ASN-GW or BS, transmitting the data messages stored in the buffer storage to target BS via a set up data channel and to MSS via an airborne interface between BS and MSS, which can reduce the cost of data and signaling between CSN and ASN and secure low lost rate of packets and low time delay of user data without changing R3 channel interface between ASN and CSN and support non-loss switch according to the requirement of service grades and service quality.