A motion/vibration detection system and method therefore are provided. The system includes a transmitter and a receiver. The transmitter includes a transmit/receive antenna unit and a first oscillator. The receiver includes a receiving unit and a demodulation unit. The transmit/receive antenna unit receives an output signal from the first oscillator and transmits a detection signal. The detection signal is reflected from at least one object under detection into a reflected detection signal, which is received by the transmit/receive antenna unit. The transmit/receive antenna unit injects the reflected detection signal into the first oscillator and accordingly the first oscillator is under a self-injection locking mode. The receiving unit receives the detection signal. The demodulation unit demodulates the detection signal received by the receiving unit into a baseband output signal, to extract at least one motion/vibration information of the objection under detection.