Abstract: In order to acquire time resolution image of -ray while impulse pulse width is under 20 ns, a new scintillator named Yb:YAG is developed, and its characteristics of luminescence decay time, excited luminescence spectrum of X-ray, relative luminescence efficiency and spatial resolution are measured. The measurement shows that there are three decay components. The fast decay constant comes to 1.2 ns, but the slow decay constant depends on radiation category. The excited luminescence spectrum ranges from 250 nm to 800 nm, and three peaks, 320 nm, 380 nm, 500 nm, exist. Meanwhile, the strongest intensity spectrum is located at 320 nm. The relative luminescence efficiency reaches 1900 ph/MeV. The spatial resolution is 2 lp/mm in the test with W resolution chart. The frequency is 0.7 lp/mm when the MTF is 0.5 in the test with edge image. The result shows that the characteristics of Yb:YAG crystal could satisfy the measurement demand.