After the asynchronous interconnection of Yunnan Power Grid (YPG) and the main grid of China Southern Power Grid (CSG), the system stability characteristics of YPG will change dramatically, and the problem of system frequency will become the main stability problem. In order to ensure the operation security of YPG after asynchronous interconnection, a series of experiments on the asynchronous interconnected system is carried out by CSG to validate the frequency control measures including the primary frequency regulation, the frequency limit controller (FLC) of HVDC, the electric power system stability control system, and the third line of defence. The experiment items from April 7 to April 9 are introduced in this paper. The main problems and cases occurred in the system experiment are analyzed, and simulation and comparison are carried out. The results show that the FLC of HVDC and the electric power system stability control system are able to adapt to the operating requirements of YPG after asynchronous interconnection, while the PID parameters of hydro trubine governors and the dead-zone settings of primary frequency regulation still need to be further optimized and regulated.