The macro-bending induced optical fiber cladding modes frustrated total internal reflection effect is used to realize the liquid level probe with a simple structure of single macro-bend polymer optical fiber loop. The test results show that the extinction ratio reaches 1.06 dB. “First bath” phenomenon is not obvious (about 0.8%). The robustness of the sensor is better, and the ability of anti-pollution is stronger compared with the conventional sensors. The process of making this sensing probe is extremely easy, and the cost is very low.