In this paper, we propose a pressure sensor based on a polymer two-mode waveguide interferometer, with its sensing performance enhanced through the introduction of an air trench layer into the substrate. The operating principle of the sensor is elucidated based on the photoelastic effect and evanescent field theory, the structure of the sensor is optimized using finite element software, and an expression for its sensitivity is presented. The results show that the sensitivity of the proposed sensor reaches 43.22 pm/kPa within the 0–100 kPa pressure range. Our proposed pressure sensor offers ad-vantages, including simple structure, high sensitivity, good linearity, as well as low temperature cross-sensitivity. These advantages make it particularly suitable for the application scenarios with complex electromagnetic environments, limited space, or high reliability requirements, such as military equipment monitoring, aerospace vehicle systems, and industrial process control.