The invention relates to a real-time adjustment system and method for controlling deformation of a rear support duct piece. The rear support duct piece is a duct piece which is subjected to a tube jacking counter-force action in a main tunnel, and the real-time adjustment method comprises the following steps of constructing a partition wall in a soil body at the rear support duct piece, using theouter surface of the rear support duct piece and the partition wall to form a sealed cavity, and surrounding the soil body at the outer surface of the rear support duct piece by the sealed cavity; during the tunneling operation of a tube jacking machine, detecting the deformation amount of the rear support duct piece in real time, dynamically adjusting the injection amount of a non-hard slurry injected into the sealed cavity according to the deformation amount, and achieving the control of the deformation of the rear support duct piece. The system achieves the effect of real-time regulation, solves the problem in the prior art that the degree of deformation of the duct piece is passively monitored without countermeasures, and avoids the occurrence of the deformation overrun condition, thereby avoiding the problem of additionally increasing the construction period and cost.