The invention relates to a manufacturing method of a 30-ounce disposable gas cylinder, in particular to a solder required for the soldering of a valve seat before the soldering of a small-scale gas cylinder and a placing method of the solder. The placing method comprises the following steps: before putting the valve seat in a bottle body, loop overlapping a manufactured oxygen-free copper wire opened solder at the root part of a conical cylinder of the valve seat; and when the valve seat is put in the bottle body, placing the solder between the valve seat and the bottle body. According to the solder and the placing method, the usage amount of the oxygen-free copper wire solder can be decreased, the soldering quality between the valve seat and the bottle body is improved, the workload of post-soldering manual filing caused by coppering is decreased and the appearance quality is improved.