Abstract: The China Spallation Neutron Source (CSNS) is the first medium and high energy, high current, high power proton accelerator in China. From the linear accelerator to the rapid cycle synchrotron, it faces a lot of challenges from the physical design of the accelerator to a large number of key technologies. On the basis of overcoming these challenges and technical difficulties one by one, we officially started construction of project in September 2011, passed the test in March 2018, and successfully completed the project construction on schedule. After the facility was officially opened to users in September 2018, the beam commissioning was done according to the plan during the user operation, and the beam power increased continuously. In February 2020, the designed beam power 100 kW was reached, and it is one and a half years ahead of schedule. The beam commissioning time for the beam reaching the design target was much less than that of similar facilities. Through further efforts, the beam power reached 125 kW in February 2022. Beam commissioning plays an important role in the construction of accelerator. The meticulous research and preparation work in the early stage and the new method developed in beam commissioning, provide a guarantee for the successful beam commissioning. After the formal user operation, the operation is stable and reliable, the beam supply time and accelerator beam supply efficiency are continuously improved, and the user running time and efficiency have reached the best level among the similar facilities in the world. The second phase of CSNS project will be started soon. In the second phase, the beam power will be upgrade to 500 kW. At present, the detailed design and the R&D of the key technologies for the accelerator upgrade have been making. This paper comprehensively introduced the design, key technical challenges and devices development of the CSNS accelerator, the beam commissioning process was also introduced, and the key problems and the corresponding solutions in the beam commissioning were described.