A design of an integrated fiber optic sensor for simultaneously measuring ammonia (NH3) concentration and gas pressure is proposed, which is based on a single mode fiber (SMF)-capillary-no core fiber (NCF) single-mode fiber (SCNS) structure. The measurement process is achieved by simultaneously monitoring the wavelength drift appearing in the transmission and reflection spectrum based on multi-mode and Fabry-Pérot interference. In achieving the desired sensor response, the NCF is coated with the zinc oxide (ZnO) film serving as the sensitive material for NH3, and a gas micro-channel is created on the sidewall of the capillary for gas pressure measurement. The experimental results indicate that the sensor with structural parameters optimization presents sensitivities of -35.52 pm/ppm for NH3 concentration and 4158.57 pm/MPa for gas pressure. The proposed sensor based on SCNS structure is capable of achieving excellent stability and consistency in the presence of mutual interference induced by simultaneous measurement of dual-parameter, demonstrating significant potential in gas measurement applications.