The invention relates to the field of communication technologies, in particular to a down link synchronizing system and method on the basis of the cross correlation of LTE-TDD downlink synchronization codes. The down link synchronizing system comprises a first antenna, a second antenna, a first LTE-TDD uplink and downlink shift switch, a second LTE-TDD uplink and downlink shift switch, an analog-to-digital conversion processing unit, a first complex mixing processing unit, a digital down-conversion processing unit, an LTE-TDD downlink synchronous processing unit, an LTE-TDD uplink and downlink switching control unit, a digital upper-conversion processing unit, a second complex mixing processing unit and a digital-to-analogue conversion processing unit. According to the down link synchronizing system and method, the LTE-TDD downlink synchronous processing unit carries out autocorrelation processing on the downlink synchronization codes to obtain control signals on the uplink and downlink shift switches, and selection of uplinks and downlinks is achieved through control over the first LTE-TDD uplink and downlink shift switch and the second LTE-TDD uplink and downlink shift switch. The system and method are easy to achieve, low in cost and high in precision.