The invention relates to an airflow preventing device used for oil-gas pipeline welding. The airflow preventing device is mainly composed of an inflating device, an air cylinder inflating pipeline, anair cylinder, a sliding supporting shaft, an air bag inflating pipeline, a universal joint, a fixed hinged support, a sliding hinged support, a multi-way joint, a centering wheel, a box body, an airbag, a ventilating hose, an air bag air escape valve, a load-bearing wheel, a fixed supporting shaft, a traction hinge and a tractor, the structure of the airflow preventing device is symmetrical about the universal joint, the inflating device is installed on the tractor and inflates the air cylinder through the air cylinder inflating pipeline and inflates the air bag through the air bag inflatingpipeline, the air cylinder, the sliding supporting shaft, the fixed hinged support, the sliding hinged support, the centering wheel and the fixed supporting shaft are all installed on the box body, the sliding hinged support slides under the action of the air cylinder through the sliding groove in the box body, so that the fixed supporting shaft is driven to be opened, and the centering wheel acts on the pipelines to achieve the centering effect. The airflow preventing device used for oil-gas pipeline welding can be used for realizing under-pressure maintenance of the in-service pipelines with cracks and other problems which occur.