This paper presents the newly designed fiber optic pressure sensor using the TR-EFPI fiber optic sensor with a single mode fiber (SMF), and a micro fabricated diaphragm. The output signal of TR-EFPI fiber optic pressure sensor can be easily analyzed based on the spliced loss based model and large deflection theory. Then, we can design the optimal length between the thin film of diaphragm and the end of single mode fiber. From these analyses, the relation between the applied pressure and the output signal of TR-EFPI fiber optic sensor can be simulated. Based on these processes, we can design the TR-EFPI fiber optic pressure sensor measuring various conditions by changing the size of thin film. As the newly designed TR-EFPI fiber optic pressure sensor can be fabricated in small size and has good sensitivity, it can be applied to medical instrument like pressure sensor and force sensor for catheter and minimally invasive surgery robot for safer surgery.