The Simulation and experimental results of single segment amplifier (SSA) used in high power laser system are introduced in this paper. By optimizing the pumping constructs of SSA, about 4.9%cm -1 small signal gain efficiency and 2.4% storage energy efficiency have been obtained when working voltage is about 22 kV. At the same time, the thermal distortion and wavefront changing are investigated, the changing of cleanliness in pump cavity is measured.