The micro-electromechanical systems (MEMS) process and packaging with poly-dimethylsiloxane (PDMS) polymer materials are important technologies in semiconductor industries. In this study, we propose using the L9 orthogonal array to determine the optimal parameters for an optical fiber sensor packaged with PDMS. According to analysis of variance results, the optimal parameters are as follows: a grating with a diameter of 60μm, a period of 650μm, and a length of 2.5cm, as well as a photoresist structure with a width of 2mm. The results of a large-the-best (LTB) analysis indicated that the expected sensitivity value of a sensor with those parameters would be around 0.0345dB⁄με. After testing and verification, the sensitivity results indicated a mean sensitivity of 0.0339dB⁄με, with the deviation in sensitivity being less than 0.14%.