Green-emitting Y3Al5O12: Tb phosphor materials have been widely studied because of their high luminescence efficiency and stability under the conditions of high irradiance with an electron beam. In this paper, Green-emitting phosphor of yttrium aluminum garnet (Y3Al5O12 or YAG) doped with Tb3+, Ce3+ and Gd3+ was synthesized by sol-gel method. By means of TG/DSC, XRD, and photoluminescence (PL) performance, the sintering condition and its influence on the powder’s emitting performance were studied. The experimental results showed that, Y2.8Tb0.12 Ce0.08-x GdxAl5O12 synthesized by sol-gel method was a kind of phosphor of good performance. When the value of x was set at 0.04, the best emitting performance was obtained. The Y3Al5O12: Tb, Ce, Gd particles had fine size, spherical shape, filled morphology, high crystallinity, and good brightness.