The invention relates to a monitoring and early warning device for a metal bellow compensator and a monitoring method of the monitoring and early warning device and belongs to the technical field of intelligent monitoring. The monitoring and early warning device comprises a pressure sensor, a temperature sensor, an axial displacement sensor, a bracket I, a bracket II, a radial displacement sensor,an analog quantity collection module, a solar panel, a storage battery, a wireless router, a data processing center, a user monitoring center, a connecting pipe I, a leakage alarm sensor, a bellows,a stress-strain sensor, a connecting pipe II, a camera and a wire, and the monitoring and early warning device is powered by a solar battery after the power is stored by the storage battery, or is powered by a power supply. According to the monitoring and early warning device, the compensator can be monitored comprehensively, whether the compensator is required to be changed or whether the compensator can be maintained to the overhaul period can be pre-judged, the problem of sudden damage of the compensator during pipe network running is solved, sudden shutdown of a pipe network due to damageof the compensator is prevented, and loss caused by shutdown is reduced; besides, the monitoring and early warning device is convenient to mount and energy-saving.