The invention discloses a river crossing construction method of a multi-pipe-segment sinking pipe. The method comprises the steps that A, underwater earthwork construction is carried out, and a groove used for sinking of a pipeline is excavated; B, a water area pipeline is assembled and jointed, afloat joining construction is carried out, and afloat water-free multi-pipe-segment welding is achieved; C, the water area sinking pipe is constructed, and the pipeline used for being spliced into a whole sinks into the groove; D, the underwater groove is subject to backfilling, the groove used for containing the pipeline is filled and leveled up, the pipeline is hidden, afloat water-free welding work is carried out, the construction difficulty is reduced, construction quality is improved, and whole pipeline sinking after the multiple pipe segments are welded is achieved.