Mercury is the most toxic and harmful heavy metal pollutant, and it is essential to detect and remove mercury from beverages. Inducing the porphyrin molecules into the chitosan structure, a novel membrane sensor tetrakis(4-carboxyphenyl)porphyrin-grafted chitosan fiber membrane (TCPP-CS) was prepared by electrospinning method and applied to recognize Hg²⁺ contaminant selectively. Compared with other common metal ions (Pb²⁺, Cu²⁺, Fe³⁺, Cr³⁺, Mg²⁺, and Zn²⁺), the colorimetric sensor has specific color development and sensitivity to Hg²⁺ and the detection limit of the sensor reaches 1 × 10^–5 mol·L^–1. The response time of the membrane is 5 s, and it can be specifically colored in various pH environments convenient for practical application. Hg²⁺ resulted in a visual color change of the fiber membrane from brown to yellow-green, indicating a potential interaction between the porphyrin-functionalized chitosan fiber membrane and Hg²⁺ ions, and the wavelength shift of the UV–visible spectrum can be observed. It has the advantages of simplicity, rapidity, high selectivity, and high sensitivity, providing a new method for removing and detecting heavy metals in traditional Chinese medicine and drinks.