The signal processing system includes a first signal processing unit, a first route, and a second route. The first signal processing unit receives a first signal and generates a first sub-signal and a second sub-signal. The first route receives the first sub-signal through one end of the first route and outputs the first sub-signal from the other end. The second route receives the first signal transmitted from the antenna through one end of the second route, and outputs the first signal through the other end. The second route includes a second signal processing unit, receives the first signal and generates a third sub-signal and a fourth sub-signal; a gain unit receives the third sub-signal to gain the first signal; and a circuit unit receives the fourth sub-signal, determines whether to enable the gain unit, or to adjust a gain level of the gain unit.