In this paper, an improved mathematical model is proposed by taking the factors of high-energy photons and temperature into consideration, which is verified and explained by the experimental data in our experiments and other papers. By fitting and analyzing the experimental data, we can quantitatively determine the relationship between the pump power $P_{\lambda }$ and the photon frequency $\nu$ in the fiber core, the core area $A$ and the temperature T of the fiber core and PD loss, and explain the mechanism of the PD phenomenon to a certain extent. We believe that the excitation of color centers by high-energy photons is the main reason for photodarkening. Furthermore, there is a positive correlation between the power of high-energy photons and the photodarkening rate, and the temperature is positively correlated with the saturated photodarkening absorption.