The flange-connected flag-type mechanical ball-through indicator is composed of a mechanical contact body and a flag indicator head. It has the characteristics of intuitive indication, automatic reset of the mechanical part, and manual reset of the display part. The indicator can be displayed normally when the pipeline passes through the pig in the forward and reverse directions. So it can be positioned on the pipeline, and the passage of the pig in the pipeline can be transmitted through the mechanical structure to provide the operator with information and guide the process flow conversion.