The invention discloses a synchronous detection device and a synchronous detection method for a frequency-hopping signal source of a microwave density detector, and belongs to the field of signal processing. According to the device and the method, a ground temperature compensation detection circuit is additionally arranged in a microstrip detection circuit to reduce the influence of temperature; asmall-package 0201 detection diode PCB (printed circuit board) is adopted for tin soldering, so that the phenomenon that a conductive adhesive is easily cracked and separated after long-term high-temperature vibration is avoided, dependence on a micro-packaging process is reduced, and the producibility is improved; behind the microstrip detection circuit, a frequency-hopping control signal of thesame source as a frequency-hopping signal source is logically processed to generate a sampling and holding clock, and an output voltage of the microstrip detection circuit is synchronously distinguished and received through a time sharing sampling circuit according to a frequency-hopping time sequence of a double-frequency-point signal source; an attenuation coefficient regulation circuit and a mode control circuit are additionally arranged, and attenuation coefficient regulation and mode switching are completed through a microprocessor to implement sharing of the same hardware circuit by a measurement mode and a calibration mode, so that circuit design and software control are simplified, the cost is reduced, and the reliability is improved.