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In this paper, a thin-walled-microsphere air-cavity (TWMAC) F-P interferometric fiber temperature sensor is proposed for high-temperature measurement up to 400 °C. The TWMAC sensing structure, which is fabricated by discharging the structure of single-mode fiber splicing with hollow-core fiber to form an air-cavity with a three-beam interference. Its interferometric operation, temperature sensing principle, and sensitization by vernier effect were analyzed theoretically and fundamentally. The sensor is fabricated by a splice machine, packaged by a copper tube and tested in the temperature range of 50–400 °C. The TWMAC has a sensitivity of roughly 3 pm/°C, while the vernier effect can increase the sensitivity up to − 18.92 pm/°C, which is 5-times more sensitive. The proposed sensor can be utilized for high temperature measurements in environments with complicated production or life processes because it is lightweight, compact, and anti-electromagnetic interference. [Display omitted] • A thin-walled-microsphere air-cavity (TWMAC) fiber sensing structure for temperature was presented. • It could achieve a high-temperature sensitivity up to − 18.92 pm/℃ by Vernier effect under the temperature up to 400 ℃. • Its sensitivity was 5 times than that of a traditional fiber F-P sensor. [ABSTRACT FROM AUTHOR]