In this paper, we proposed an in-fiber Fabry-Perot temperature sensor which filled with Indium gallium stannum (InGaSn) alloy. By splicing a single-mode fiber axially with hollow-core fibers (HCFs) of varying inner diameters, a cavity of the Fabry-Perot interferometer (FPI) structure is formed. Assisted by liquid metal with fluidity and high thermal expansivity, subtle temperature fluctuations are converted into variations in the interferometric cavity length which leads to a significant spectral drift. Experimental result shows that the temperature sensitivity for the proposed sensor reaches 11.3 nm/°C in the range of 30-40°C, which is almost an order of magnitude higher than that of other extrinsic FPIs. Such high sensitivity within this temperature range makes the sensor potentially applicable in temperature monitoring in the vitro cell culture and biopharmaceutical fields. Additionally, influences caused by the inner diameter of HCFs and the amount of liquid metal filled in structure are also considered in this work.