A tin suction gun comprises a gun head, a shell, a trigger, a tin storage barrel and a rear seat. The gun head is arranged at the front end of the shell and comprises a heater and a tin suction pipe. The tin suction pipe is connected with one end of the tin storage barrel, and the other end of the tin storage barrel is connected with a negative pressure generator. A multi-gear switch is arranged in the trigger. A locking button is arranged on the shell and comprises a button handle and a rotary pin, and the rotary pin is embedded into an ejector block. The rear seat is composed of a seat sleeve and an inner seat body, a rear seat spring is arranged between the seat sleeve and the inner seat body, and the inner seat body comprises a tin storage barrel connector and an air pipe connector. The air pipe connector is connected with the negative pressure generator through an air pipe, and an isolating screen is arranged on the inner seat body. A limiting groove is formed below the inner seat body, and a locating screw penetrates the limiting groove to be fixed to the bottom of the seat sleeve. A locating hole is further formed in the bottom of the seat sleeve, and the upper end of the ejector block is matched with the locating hole. According to the tin suction gun, the problem that a tin storage barrel in the prior art is prone to falling off is solved, and the tin suction gun is good in reliability, comfortable in hand feeling and convenient to use.