The invention relates to a portable sampling gun. The defects that a sampling device for sampling flue gas in the prior art is unreasonable in structure and inconvenient to operate is overcome. According to the portable sampling gun provided by the invention, a fixed plug and a fixed flange are arranged on a gun body in a sleeving way; an elastic gasket is arranged on the fixed flange; a straight ruler is arranged on the gun body; the fixed plug comprises a first half part and a second half part; the fixed flange comprises a third half part and a fourth half part; and the third half part and the fourth half part are fixed through a connecting piece. According to the scheme, the sampling gun is very convenient to mount, the sampling gun is fixed on a flue and the use performance of the sampling gun is optimized. In addition, the straight ruler is arranged on the gun body, and the length, stretching into the flue, of the gun head can be observed intuitively through the straight ruler, so operation of technicians is benefited and the use performance of the sampling gun is further optimized.