The reliability tracing techniques is one of the most effective methods to identify the weak parts of a power system. The contribution of each component towards system reliability can be evaluated using the reliability tracing rules and models. Greater contribution means higher impact on system reliability. These components can be recognized as weak parts of the system. The reliability tracing principles and reliability tracing indices are analyzed， the improvement measures based on the reliability tracing results are presented. The robustness and economy of the improvement measures are evaluated using the constant annuity method. The reliability contributions of the individual components in 2010 Guangdong power grid are calculated using the reliability tracing principles. The weak parts which have the most impacts under two typical operating modes are identified. The reliability improvement measures based on the component reliability contributions are presented， and further evaluated by using the cost-benefit analysis.