Here, the real time pyrolysis characteristics, the degradation degree and the aging time of the transformer oil have been investigated using laser induced fluorescence (LIF) spectroscopy. The signal elevation up to four-fold and the lucid red shift up to 10 nm are obtained against those of fresh oil. The fluorescence signal and the corresponding spectral shift are demonstrated to follow a linear correlation in terms of aging time. It mainly arises from the gradual alteration of the fluorescence properties of the transformer oil's aromatic rings during steady operation of the power transformer. In fact, the degraded oil undergoes the transition from mono cyclic aromatic rings to poly cyclic ones as well as the abundant poly cyclic rings with the aging time. Moreover, the fluorescence parameters obviously elucidate the real time competence of LIF to assess various degrees of oil degradation via steady sampling in the operational power transformers. Furthermore, the empirical findings are supported by FTIR, TGA and UV-PL accompanying the fluid mechanical/chemical routine tests. FTIR spectra and TG analyses, alongside the other characteristic measurements strongly indicate the increasing population of aromatic hydrocarbons, and the elevation of the activation energy in terms of aging time.