The invention discloses a geologic advanced detection method based on an alternative power supply and full-section tunneling machine, and the method comprises the steps: (1), providing a geologic advanced detection system, wherein the geologic advanced detection system comprises a tunneling machine, a constant current source, a programmable relay and an optical fiber current sensor, which are all located in a tunnel, and the tunneling machine comprises a shield, a knife disc, and a main drive bearing connected with the shield and the knife disc; (2), switching the applying position of a current of the constant current source by a preset period, so as to enable the constant current source to alternatively supply power to the shield and the knife disc, and measuring corresponding voltages; (3), calculating the apparent resistivity of a side geologic body and the apparent resistivity of a front geologic body of the tunneling machine according to the Kirchhoff's Current Law and the relation between the voltage and current, and analyzing the geologic conditions of the side and front geologic bodies.