The invention discloses a novel manufacturing method of a large-diameter inclined tee joint. The novel manufacturing method comprises the following specific steps of A, manufacturing forming of an inclined tee joint pipe fitting, B, positioning welding of the inclined tee joint pipe fitting, C, preheating of an inclined tee joint fitting tee joint inclined branch pipe and a tee joint straight main pipe, D, joint first layer welding of the inclined tee joint fitting tee joint inclined branch pipe and the tee joint straight main pipe, E, joint bottoming welding of the inclined tee joint fitting tee joint inclined branch pipe and the tee joint straight main pipe, F, joint secondary preheating of the inclined tee joint fitting tee joint inclined branch pipe and the tee joint straight main pipe, G, joint welding of the inclined tee joint fitting tee joint inclined branch pipe and the tee joint straight main pipe, H, inclined tee joint fitting low-temperature protecting, and I, inclined tee joint fitting heat treatment. The novel manufacturing method of the large-diameter inclined tee joint is simple in manufacturing process, low in cost and capable of solving the quality flaw problem probably existing in the large-diameter inclined tee joint.