The invention discloses a bidirectional rotary joint with a balance mechanism. The bidirectional rotary joint is characterized in that mandrels of two rotation pairs are fixed on a support, and when the two rotating pairs are arranged in middle positions, axes of connecting rod shaft heads on rotatable outer cylinders of the two rotating pairs coincide; and multiple adjusting holes are formed in end covers of the outer cylinders, springs and adjusting plates are arranged on the mandrels in a sleeving mode, inner rings of the springs are fixed in positioning grooves in the mandrels, the adjusting plates can rotate on the mandrels, pin holes are formed in the adjusting plates respectively, pins penetrate through the pin holes respectively, and are inserted into the adjusting holes in the endcovers, and outer rings of the springs fixedly hook on the pins. The bidirectional rotary joint is used in a rod-shaped serial connection mechanism, and rod pieces can do two-way rotary motion; whenthe rotating pairs are in the middle positions, the axes of the front rod piece and the rear rod piece coincide, so that the occupied space of the mechanism is small; when the rotation of the rod pieces need force to balance, torsion of the springs can be conveniently adjusted to provide balance force; and according to the bidirectional rotary joint, the performance of the rod-shaped serial connection mechanism can be remarkably improved, and especially the performance of mechanisms such as an endoscope support and the like can be remarkably improved.