In organic semiconductors, photophysical properties are closely related to the exciton transition (ET). Therefore, modulating ET has great significance for the photophysical properties enhancement of organic semiconductors. Researchers can modulate the ET in organic semiconductor crystals and films by applying high pressure and annealing processes which respectively affects the molecular distance in crystals and the molecular orientation in films. Yet, how to simplify the way of modulating ET in organic semiconductors remains a great challenge. Herein, we prepared 3,4,9,10-perylenetetracarboxylic dianhydride crystalline films and nanorods, and successfully modified the type of the governing ET in PTCDA crystallites so that realized the switch of emission wavelength. Particularly, we exploring ET modulation mechanism. This will be helpful for the photophysics increment of organic semiconductors.