A foam caulking gun comprising a gun body (1), a fluid inlet valve (2), a fluid outlet valve (3), and an opening/closing apparatus (4). The fluid inlet valve comprises a fluid inlet channel (21), a sealing element (22), and a return spring (23). The sealing element and the fluid inlet channel are sealed with each other while a sealing opening (210) is formed within the fluid inlet channel. A sealing strap (220) is formed on the sealing element. A pushing element (5) used for pushing downward the sealing element is arranged within the fluid inlet channel above the sealing opening. When the pushing element is subjected to a downward thrust, the pushing element pushes downward the sealing element to open the fluid inlet channel, thus allowing the pushing element to control the sealing strap and the sealing opening to maintain therebetween a stable spacing. When the sealing element is not subject to a downward thrust, the restoring force of the return spring causes the sealing element to seal off the fluid inlet channel. The foam caulking gun is capable of generating frontal foaming, foams uniformly, and has a foaming material of a large volume.