Abstract: Composition, principle and process of the gas starting system of Solar Taurus 70 gas turbine are described in this paper. Common causes for the system failure are analyzed from aspects of program and hardware. By the troubleshooting method, it is confirmed that the improper location of pilot control spring of pressure regulating valve in the gas starting system is the primary cause for start failure of the gas turbine. According to the structure and working principle of pressure regulating valve, the accuracy of fault analysis is verified. Finally, improvement measures are proposed in view of the performance monitoring of the gas starting system. Although the failure of the gas turbine can be easily treated, the systematic analysis and conclusion in the cause investigation can provide a reference for troubleshooting of the gas starting system of similar gas turbines.