Disclosed is a portable fire extinguishing device, which comprises a casing (1) and a cartridge (2) provided inside the casing (1). The device is characterized in that: the casing (1) comprises a first half casing (4), a second half casing (5) fitted to the first half casing (4), a fastening ring (6) and a bottom cover (7); the first half casing (4) and the second half casing (5) are butted; the fastening ring (6) is provided on the top ends of the first half casing (4) and the second half casing (5) so as to fasten the both; and the bottom cover (7) is provided at the bottoms of the both. The first half casing, the second half casing, the fastening ring and the bottom cover are clamped and fixedly connected with each other to form a whole casing so that the whole wall thickness of the casing is uniform, thus improving injection moulding processes, reducing the difficulty in manufacturing a mould, saving plastic resources, and facilitating installation and disassembly.