The invention discloses a tunnel advanced detection system and detection method based on double-channel amplitude modulated waves. The system comprises a signal generation module, double paths of constant current source modules and a fiber current sensor. The signal generation module generates two paths of amplitude modulated waves with different carrier frequencies and inputs the amplitude modulated waves into the constant current source modules respectively. The output current of one constant current source module is directly connected to a shield and the other constant current source moduleinversely passes through a fiber ring and connected to the same point of the shield together with the first constant current source module. The sensing fiber ring winds a main driving bearing. The grounding ends of the constant current source modules are connected to anchor rods in a certain distance behind the tunnel. The output signals of a fiber current sensor are subjected to band-pass filtering, envelope detection and A/D sampling, and then current of the shield and a knife disc are obtained simultaneously. Compared with the traditional single-direction power supplying and alternative power supplying, a problem is solved that a measurement coefficient of the fiber current sensor is changed along with the time and detection reliability of the system is improved.