The invention relates to a liquid level sensor based on POF (plastic optical fiber) optical fiber macrobending. The liquid level sensor comprises a single macrobending optical fiber annular structure and a fixing structure, wherein the single macrobending optical fiber annular structure is manufactured through bending POF bare optical fiber and has the top macrobending radius being 2.5mm, the top macrobending part of the single macrobending optical fiber annular structure is used as a probe, two tail ends of the POF bare optical fiber are provided with optical fiber joints, the fixing structure is used for encapsulating the single macrobending optical fiber annular structure, and the probe is exposed out from the fixing structure. The liquid level sensor has the advantages that the design of the single macrobending optical fiber annular structure is adopted, the optical fiber macrobending is singly used for enhancing the CMFTIR (cladding mode frustratedtotal internal reflection) effect, the distinction degree being 1.06dB is realized, and the liquid level measurement requirement is met. In addition, the double optical fiber coupling is not needed, so that the process difficulty is simplified, the structure is more compact, and the liquid level sensor is suitable for being used in a narrow space. Meanwhile, the liquid viscosity of an SMBFL (single macro-bend fiber loop) structure is low, the initial bath error is greatly reduced, the SMBFL directly detects bright field signals with higher power, and the requirement of long-distance transmission is met.