Taking advantage of multi-angles light paths in end-pumped slab amplifier, a measurement system of characteristic factors of end-pumped slab amplifier is established, which can accurately detect the extracted power, wavefront distortion and depolarization at the same time. This system contains a kilo watt level and narrow linewidth seed source, highly accurate detectors of thermal induced wavefront distortions and depolarization. When the seed source is 2.7 kW and the pump current is 90 A, the extracted power from the slab amplifier is about 2.9 kW, the wavefront distortions is less than 1 μm (aperture of 27 mm), and the depolarization is about 5.1%. Compared with the factors under the non- extraction, the differences between them are distinct, which proves that the detecting system is essential to accurately acquire the qualities of slab amplifiers.