In this work, 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl) methylene]-nonitol (TBPMN) was conscripted as the clarifying agent, the influence of the injection pressure on optical properties of PP were investigated, and results documented that increasing the injection pressure could not improve the transparency of the transparent PP. Thereafter, the crystallization behavior and morphological changes of transparent PP in condensed structure under different injection pressures were studied by the differential scanning calorimetry (DSC), the scanning electron microscopy (SEM) and the dynamic thermomechanical analysis (DMA), respectively, and results presented that change in injection pressure influence crystallization properties significantly. Besed on analyzing of the relationship between structure and optical properties, the effect of pressure on the optical properties was explained as follows: low injection pressure would be facilitated to the transparency of transparent PP, because under low injection pressure, the clarifier fiber could be dispersed uniformly and the network structure was formed and preserved well, and molecular chains of transparent PP was crystallized to the nanometer-level fiber on the surface of nucleation sites, which greatly reduces the scattering of light. However, increasing the injection pressure would promote the fiber itself accumulation into a scatterer point, which not only reduces the effect of the clarifier, but also causes the preferential arrangement of the PP molecules to produce an oriented structure due to strong external force and shearing action, thereby increasing light scattering. © 2020, The Polymer Society, Taipei.