Large-capacity controllable shunt reactor（CSR）has been applied to the 750kV northwest 2nd power transmission channel project.Capacitive current is the main factors affecting the performance of differential protection used for extra high voltage（EHV）long line，and distributed capacitive current and shunt reactor current should be calculated and compensated completely.As the capacity of CSR is greatly variable in operation，the practice of indirect calculation of CSR current with its parameters will result in over-compensation or under-compensation.To achieve accurate compensation results，the CSR current is directly introduced into line protection.The problems for attention in engineering application are discussed as well.Digital simulation test is performed to verify the validity of theoretical analysis.This method has improved the sensitivity and reliability of line protection and is successfully used in real projects.