5-(4-Carboxyphenyl)-10,15,20-triphenylporphyrin (TPP) is a porphyrin derivation with high symmetry and conjugated π bond. Porphyrins are critical precursor of many bio-compounds, such as heme and chloroplast. And its unique structure contributes to a special spectroscopy. In this article, the effect of polarity and pH of solution on the optical property of TPP was analyzed by detecting the absorption and emission spectra in different solvent. Then, we discussed how the molecular structure changed before and after protonation by theoretically circulating several basic parameter of different conformations. Finally, we predicted its prospects for photodynamic therapy according to the photodynamic reaction efficiency shown in vitro.