Abstract: To improve the pressure sensitivity of side-hole fiber grating sensors, a side-hole sensitization structure was designed. Based on the finite element analysis method, a temperature & pressure sensor model of the sensitization structure was established, and the influence laws of sensitization structure parameters on pressure sensitivity of the sensor were studied through simulation analysis; using the response surface optimization design method, combined with polyurethane materials, a sensor prototype was fabricated, and its performance was experimentally verified. The results indicate that the pressure sensitivity of the designed sensor is 202.41 pm/MPa, and the temperature sensitivity is 34.627 pm/°C, representing improvements of 18 times and three times, respectively, compared to the sensor without the sensitization structure. In addition, to address the harsh downhole environment, a protective structure for the sensor was designed, and its feasibility was verified. The study shows that the sensitization design scheme significantly improves the performance of the side-hole fiber grating sensor and provides a new method for highly sensitive downhole combined measurement of temperature and pressure.