The invention relates to a bladder-type conveying device and a conveying method thereof. The bladder-type conveying device comprises a material box, a first material output pipeline and a first cam rotor pump, wherein the first material output pipeline and the first cam rotor pump are located on the material box. The first material output pipeline is connected with a balance tank which is internally provided with a bladder bag. The bladder bag is connected with a water box which is provided with a second cam rotor pump through a water pipe. The balance tank is connected with a pressure box which is provided with an output pipeline through a second material output pipeline. The first cam rotor pump and the second cam rotor pump are connected with a controller. According to the bladder-type conveying device, materials are sent to the balance tank, the bladder bag in the balance tank receives water and returns water from the water box, the first cam rotor pump and the second cam rotor pump are in alternate operation, and the materials in the balance tank are conveyed to the pressure box and finally output; and a sectional type pressurizing mode is adopted, pressure demands on the first cam rotor pump do not exist, water supplying, pressurizing and expanding are conducted on the bladder bag through the second cam rotor pump, the bladder bag extrudes an inner cavity of the balance tank to complete material supplying and pressure maintaining of the pressure box, and demands for rotor pumps are greatly reduced.