Provided is an improved butterfly valve. The improved butterfly valve comprises a valve body. An upper attachment is arranged at the upper end of the valve body, and a lower attachment is arranged at the lower end of the valve body. A rotatable valve rod sequentially penetrates through the upper attachment and the valve body and then enters the lower attachment. A dish plate used for opening and closing is arranged on the portion, located inside the valve body, of the valve rod. The inner walls of the two sides of the valve body are each provided with a mounting groove. Rotatable air bag assemblies are arranged in the mounting grooves. Each air bag assembly comprises a metal expansion pipe with the side edge being opened, a sealing air bag arranged inside the metal expansion pipe, connecting pieces arranged at the two ends of the metal expansion pipe, and a gear arranged at the outer sides of the connecting pieces. The valve rod is provided with gear plates engaged with the corresponding gears. The gear plates rotate along with the valve rod and further drive the gears to rotate. According to the improved butterfly valve, the sealing property is greatly improved through flexible attached sealing of the sealing air bags and the periphery of the dish plate; and meanwhile, after the dish plate is opened, the sealing air bags do not make contact with media in a flow channel, frictional losses are avoided, and the service life is long.