The present invention belongs to electric power engineering field, and provides a symmetric method for obtaining line-transferred linear active power flows in Multi-Terminal Direct Current (MTDC) power networks, which comprises: firstly establishing a system of symmetric linear indeterminate equations of buses' injection active powers in terms of buses' voltage offsets; then establishing a symmetric linear matrix equation of buses' voltage offsets in terms of buses' injection active powers and obtaining each bus' voltage offset and bus' voltage of the MTDC power network according to the system of symmetric linear indeterminate equations; finally establishing a symmetric linear relationship that expresses a line-transferred linear active power flow in terms of buses' injection active powers and obtaining each line-transferred linear active power flow of the MTDC power network according to the symmetric linear matrix equation of buses' voltage offsets in terms of buses' injection active powers, known line-transferred non-linear active power flow and inherent operation features of the MTDC power network. The method of the present invention reliably produces accurate results, and not only fast enough for real-time operation regulation of arbitrarily completed MTDC power networks but also applicable for widely varying operation states of them.