Abstract:Relay protection devices are critical to the safe and stable operation of the power system, and the accuracy of the protection device''s setting value depends on the protection setting value setting software for repeated and careful calculation of various operating modes of the grid and various faults. The actual operation mode often exceeds the offline setting method, which makes it difficult to ensure the accuracy of the current setting calculation software based on offline mode. A new on-line relay protection setting software is proposed and implemented. Rely on online tuning technology based on cloud and thin clients, distributed parallel online tuning computing architecture based on multi-threading and cloud computing, The main function modules are graphical modeling, parameter calculation, online setting and system management .We achieve the goal of on-line relay protection setting.The software has been applied in practical power network successfully，which shows a good practicality.