Aiming to the problem of the complicated preparation of existing optical fiber fluorescence temperature sensing probes, we propose a simple, cost-effective, and high-performance optical fiber fluorescence temperature sensor based on a capillary liquid core. Firstly, a mixed solution consisting of temperature-sensitive rhodamine B and temperature-insensitive rhodamine 123 was used as the temperature-sensitive material and encapsulated in a stainless-steel capillary to prepare a sensing probe. The ratio of the fluorescence emission peak intensities of the two dyes was utilized for temperature sensing. Subsequently, the sensing probe’s mixed solution concentration and capillary structural parameters were optimized. Then, the performance of the sensor was tested. Finally, the sensor was applied to real-life temperature measurements. The experimental results demonstrate that the sensor has a temperature response range of 30-70 °C and that there is a quadratic correlation between the fluorescence intensity ratio and the temperature, with the fitted correlation coefficient as high as 0.9984. The sensor exhibits excellent accuracy, repeatability, and stability, with more than three months of service time. Moreover, it can be well-utilized to detect temperature in daily life. The optical fiber fluorescence temperature sensor shows significant potential for real-time monitoring and remote detection applications.