Droop control is an effective method for realizing system energy distribution of a ship DC microgrid. In traditional droop control, the line impedance between the micro-sources in the system is inconsistent, which leads to inconsistency of the power of the distributed micro-sources. In serious cases, the micro-source DC converter even can suffer overload failure. To solve the problem of load current sharing accuracy caused by line impedance in a marine DC microgrid, a method of detecting line impedance by low frequency injection is proposed. This is achieved by injecting low-frequency AC signals into the inductance current, detecting the converter voltage and current information after injection, and obtaining line impedance by Fourier Transform. Then the droop gains can be compensated. This method can enhance the voltage quality of the DC bus in a microgrid system, improve the load sharing effect of a DC converter in parallel current sharing, and exert little influence on the stable operation of the system. Finally, the simulation results verify the effectiveness of the proposed method. This work is supported by National Natural Science Foundation of China (No. 51709028 and No. 51979021), Natural Science Foundation of Liaoning Province (No. 20170540082), and the Fundamental Research Funds for the Central Universities (No. 3132019317).