Droplet-driven triboelectric nanogenerator (TENG) with reversible switching capability has been widespread concerned; particularly magnetically controlled solid-liquid TENG, due to its fast and highly reversible responses. Herein, a hierarchical composite structured magnetic polymer surface (HCSMPS) is developed using template method and magnetic field induction, and construct a HCSMPS-based TENG (HCSMPS-TENG). The HCSMPS-TENG shows different states—fallen, upright, and no magnetic field—when applying different magnetic fields. The wetting properties of HCSMPS under three states vary significantly. The current output of the HCSMPS-TENG driven by deionized water and potassium chloride (KCl) solution varies across these states due to changes in the droplet contact area. As KCl concentration increases, the current signals of the HCSMPS-TENG initially rise due to the increased free charges but subsequently decrease due to a screening effect caused by ion adsorption. For practical application, a real-time monitoring system is developed for KCl concentration based on the HCSMPS-TENG, integrating a convolutional neural network. This system, equipped with a compact current collection circuit capable of remote data transmission and a user-friendly interface developed with LabVIEW, achieves 98.64% recognition accuracy. The HCSMPS-TENG is applied to intravenous potassium supplementation, demonstrating its potential for medical KCl concentration and infusion flow rate monitoring.