The invention provides a TDD (time division duplexing) system-based fault diagnosis device. The TDD system-based fault diagnosis device comprises a transceiver plate, a power amplifier plate and a radio frequency connector connected between the transceiver plate and the power amplifier plate; the TDD system-based fault diagnosis device is characterized in that the transceiver plate comprises a digital processing and main control module, a main board signal sending link module, a main board signal receiving link module and a radio frequency switch, wherein the radio frequency switch is used for opening and closing an sending channel and a receiving channel of the transceiver plate according to a control signal from the digital processing and main control module; the digital processing and main control module is used for monitoring the signal power of the receiving channel under the condition that RRU (radio remote unit) equipment has a fault and judging whether the difference value between an estimated value of full link signal power and a signal power monitoring value of the receiving channel exceeds a threshold value or not. The TDD system-based fault diagnosis device facilitates the remote or unpacking positioning or fault removing of an equipment fault, and the area, power consumption and cost occupied by a detection link can be saved.