For AC and DC operating system Low Frequency Oscillation (LFO) Analysis, DC system usually adopts electromechanical transient model. This paper introduces the DC electromechanical transient and electromagnetic transient model, and then establishes the electromechanical transient model and the electromechanical-electromagnetic transient hybrid simulation model on the Advanced Digital Power System Simulator (ADPSS) platform for the LFO analysis respectively. Adopting the total least squares method-rotational invariance techniques of signal parameter estimation (TLS-ESPRIT) algorithm, the oscillation power after failure is analyzed. After extracting the LFO dominant oscillation frequency and damping ratio for making the modal analysis, it compares the LFO analysis results of the two simulation models. Results of the EPRI36 standard test system and a practical power system simulation show that the simulation results of two simulation models are tallied, besides, the LFO analysis result is basically the same. The electromechanical transient model has a high practical value.