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We study the photodarkening effect in a double clad ytterbium-doped silica fiber fabricated by modified chemical vapor deposition and solution doping.A common measurement technology for photodarkening is used to study the photodarkening-induced absorption spectra.We present a fast and simple method to observe the PD effect by measurement of the fluorescence spectra.The method proposed here can be used to observe the influence for a short time,and thus reduces the requirements of system stability and heat management.It is obtained that under the condition of 45.5％ Yb ion inversion level,photodarkening-induced excessive loss at an equilibrium state is above 4.5dB/m and florescence intensity degradation is above 10％ after 500min pumping at 1041 nm for the home-made normal Yb/Al co-doped silica fiber.