The invention relates to a fluid pipeline paint supply system capable of automatically changing color, metering and spraying and a corresponding paint supply method. The fluid pipeline paint supply system comprises multiple paint supply systems, a fluid disc assembly, a metering cylinder module, a spraying robot module, a feed pipe, and a return pipe; the fluid disc assembly comprises a color change valve, a color change valve manifold, and a fluid valve set manifold; the metering cylinder module comprises a metering cylinder body and multiple plunger pumps; the metering cylinder body synchronously drives the multiple plunger pumps to complete feed and discharge actions; the spraying robot module comprises multiple spray guns and a spray gun manifold; and multiple paint supply systems, thecolor change valve, the color change valve manifold, multiple plunger pumps, multiple spray guns, the spray gun manifold and multiple paint supply systems are sequentially connected by means of the feed pipe and the return pipe. The whole flow channel and related valve sets are redesigned and arranged to form closed-loop spraying, so that the paint cost is lowered, the spraying quality is improved, and the defect of spraying breakage caused by air generated in a pipeline due to higher speed during plunging is overcome.