Abstract: The 3.5-cell direct current-superconductive (DC-SRF) photoinjector requires a 1.3 GHz 20 kW continuous wave (CW) power amplifier. The RD of a solid state amplifier (SSA) consisting of 88 unit modules with individual power supplies, which is the first high power (10 kW) CW L-band SSA in China, has been carried out under the cooperation of Peking University and Beijing BBEF Science Technology Co. Ltd.(BBEF). The RF test results show that the main parameters of this SSA reach the designed values. The efficiency is 34% at full output power of 20 kW and the gain is higher than 85 dB. The phase shift and gain vary within 9.5 and 1.6 dB respectively when the output power changes from 1 to 20 kW. It has been put into operation for more than 2000 h. After a brief description of the design, this paper mainly introduces the commissioning process of the SSA and discusses the problem of full reflection.