The invention discloses a method for installing an extra long circular tube with inclined steel structure in a hanging mode. The method for installing the extra long circular tube with the inclined steel structure in the hanging mode is used for splicing and installing of a plurality of sections of circular tube bodies and comprises the following steps that a first supporting base and a second supporting base are installed at the top of the next section of circular tube body in advance, and a fixing block is installed in the position, corresponding to the first supporting base, at the bottom of the previous section of circular tube body; a total station is erected on a floor of a completed building structure, and a prism of the total station is installed on the tube top of the previous section of circular tube body; a hoisting device is adopted to hoist the previous section of circular tube body to the position above the next section of circular tube body, an axial jack is installed onthe first supporting base, and a radial jack is installed on the second supporting base; according to data measured and obtained by the total station, the hoisting device, the axial jack and the radial jack operate to conduct fine adjusting on the inclined angle, the axial distance and the radial distance of the previous section of circular tube body; a temporary fixing device is installed at thebottom of the previous section of circular tube body and the top of the next section of circular tube body; the previous section of circular tube body and the next section of circular tube body are welded in a butting-joint mode; and the circular tube after abutting joint is finished and the completed building structure are connected and fixed.