The low melting point metal plugging method is a method to heat Bi base low melting point alloy in the well and form a metal packer inside the casing by melting, so as to realize the stable and reliable plugging of underground carbon storage and abandoned well. To study the feasibility of this method, this paper investigates the sealing performance between the low-melting-point alloy and the casing, constructs a low-melting-point alloy plug forming test and gas sealing test device, conducts experiments on the pressure-bearing capacity and gas sealing performance of the low-melting-point alloy plug combined with the casing, and analyzes the microstructure of the sealing surface using an optical microscope. The influence of axial pressure and environmental temperature on the sealing performance of the plugging barrier is also studied. The experimental results show that the performance of the formed plugging barrier is greatly affected by the environmental temperature. With the increase of the environmental temperature, the bonding ability between the Bi-based alloy plug and the casing decreases, and its pressure-bearing capacity decreases. Applying axial pressure during the solidification and forming process of the plugging barrier helps improve the pressure-bearing and gas sealing capabilities of the Bi-based alloy plug. After the alloy plug is pushed, it will experience shear damage and movement against the inner wall of the casing, but its gas sealing performance will not be completely destroyed. The research results indicate that Bi-based alloy, as a new type of material for downhole casing plugging, can achieve casing plugging through the expansion of the material itself, providing theoretical support for the new method of downhole low-meltig-point metal plugging casing.