A signal transmission method in a Time Division Duplex (TDD) system is disclosed. The method comprises following steps: within a time length of a half-frame of a radio frame, base station transmits signal on a downlink special time slot, thereafter does not transmit signal on a Guard Period (GP), and then receives signal on an uplink special time slot; all time lengths of other uplink or downlink normal time slots for transmitting signal are equal; the total time length of the downlink special time slot, the guard period and the uplink special time slot is integer times of the time length of an uplink or downlink normal time slot. In addition, a frame structure adopted in the TDD system which corresponds to the method is disclosed. The present invention makes it flexible to set the duration of the GP and it is guaranteed that, even if a synchronization signal adopts power promotion, it will not bring great interference to uplink reception of other base stations; in addition, the utilization efficiency of the system is improved.