Persistent spectral hole-burning is reported for the organic guest molecule 5, 10, 15, 20-tetra-(p-methoxyphenyl) porphin (TMP) imbeded in polymethylmethacrylate (PMMA) host at liquid helium temperature. The effects for power saturation of hole depth and power broadening of hole width were observed. Hole growth dynamics was investigated and the process of light induced hole erasing was measured. Theoretical fits to the experimental data were carried out and hole burning mechanism of the system was discussed.