In order to estimate the landing gear system stability, the first domestic shimmy test on landing gear were implemented, where shimmy modes of landing gear were excited by the plank fixed on the runway. Based on mode lobe separation combined with least square method, the test data were analyzed through identifying the modal parameters. The method was validated by simulating data with theory solution, and applied to analyze certain shimmy test data. The results show that landing gear shimmy does not occur in the flight test, which indicates the landing gear is stable.