Submarine pipeline expansion bend connecting method suitable for high-precision underwater in-place control

The invention relates to the technical field of ocean engineering and discloses a submarine pipeline expansion bend connecting method suitable for high-precision underwater in-place control. The submarine pipeline expansion bend connecting method comprises the following steps that S1, a temporary pipe section with a corresponding length is prefabricated according to the size of an expansion bend along the axial direction of a pipeline; S2, the temporary pipe section is connected with a submarine pipeline through flanges at the two ends of the temporary pipe section on a pipe laying ship, and the temporary pipe section and the submarine pipeline are laid and installed at the same time; S3, after the submarine pipeline is installed on the seabed in place, a diver or an underwater robot is adopted to remove the temporary pipe section by dismantling the flanges; and S4, after the temporary pipe section is removed, the prefabricated expansion bend is located at the reserved position after the original temporary pi