The invention provides an outer diameter adjustable reamer based on a helical fluted disk and relates to the technical field of cutting tools. The outer diameter adjustable reamer based on the helicalfluted disk comprises a tool bar. Blades are slidably connected to the interior of the tool bar. The top end of each blade is fixedly provided with a saw blade. A rotary disk is rotatably connected to the upper portions of the blades in the tool bar. The bottom end of the rotary disk is provided with helical teeth. The periphery of the rotary disk is fixedly provided with a gear. The front end ofthe tool bar is fixedly provided with a sleeve. Through the outer diameter adjustable reamer based on the helical fluted disk, the appropriate outer diameter of the blades can be adjusted according to different pore diameters so that the single reamer can adapt to machining holes with the different pore diameters, the purchase cost is reduced, and the trouble of repeatedly selecting the reamer isavoided. When the reamer reaches a certain rotating speed, oil in an oil delivery pipe flows out to achieve the lubricating and cooling effects on the reamer, abrasion to the reamer is reduced, and the machining precision is improved.