Rolling up 2D atomic layered materials into 1D nanotubes gives rise to fascinating properties due to their lower dimension, higher anisotropy, and strain effects. In this work, the curving of 2D graphitic C3N4 (g-C3N4) sheets into 1D nanotubes is demonstrated for the first time through simple and clean ultrasonic treatments. The steady-state optical transitions are slightly enhanced while the localized trapping of excited carriers is considerably suppressed after rolling up the planar sheets into nanotubes. The mechanical method to modulate the dimension scarcely changes the chemical structures, enabling the pure investigation on shape-induced physical effects. As a proof of principle, this work confirms the dynamics of excited carriers, and the photoelectronic properties of 2D semiconductors can be significantly engineered by a simple morphological evolution.