We have reported a hexaphenylsilole/polymethyl methacrylate (HPS/PMMA) composite film with a lotus-leaf-like structure shows highly stability and excellent sensitivities for metal ions (Fe3+ and Hg2+) a few years ago. In the above paper, it was considered that the special surface morphology is the important aspects which enhance the stability of the sensor. But it is still a lack of research on the sensing mechanism. In this paper, the sensing mechanism of fiber membrane is continuing to study in detail. The experimental results show that the electron-transfer mechanism is a crucial factor for the fluorescent quenching.