Addressing the issue of temperature cross-sensitivity in fiber optic microcavity salinity sensors, a novel design featuring an open saltwater cavity constructed from a ceramic ferrule and zirconia sleeve has been developed. The positive thermal expansion coefficient of zirconia effectively counteracts the negative thermal and optical coefficients of seawater, thereby compensating for temperature fluctuations in salinity measurements. To enhance salinity detection sensitivity, the open saltwater cavity is paired in parallel with a closed air cavity. This configuration precisely controls the free spectral range of both cavities, inducing a vernier effect that significantly boosts salinity sensitivity through this phenomenon. Experimental data indicate that the temperature sensitivity of the newly designed saltwater cavity is just 0.025 nm/℃, substantially lower than the -0.35 nm/℃ sensitivity due to seawater's thermal and optical properties. Furthermore, within a salinity range of 0 to 3%, the sensitivity of the dual cavity system reaches 0.180 8 nm/%, which is 10.5 times greater than that of a single saltwater cavity. The sensor offers benefits such as ease of manufacturing, high sensitivity, and robust stability. Complete temperature compensation is theoretically achievable with this setup.