[Objective] In order to investigate the change of soil quality and provide scientific basis for ecosystem health assessment, the community structure and seasonal change of soil fauna were studied in farmland-transformed tea plantation. [Methods] A farmland-transformed tea plantation in Mingshan, which is located in the hilly region of Western Sichuan Province, was chosen as research plot. In which, soil macrofauna were picked up by hand; mesofauna and microfauna were separated and collected from the soil samples by Baermann and Tullgren methods. [Results] Acarina(A), Nematoda and Collembola(C) were the dominant groups in the farmland-transformed tea plantation. The density, number of group, Shannon-Wiener index, index of density-group number and community complexity of soil fauna were all lower than the corresponding values observed in farmland. However, A/C value of soil fauna community of tea plantation was significantly higher that of farmland. The maximum values of group number, individual number and index of density-group number appeared in Autumn. These indices showed an unimodal curves and the variance among seasons were greater than that between farmland and plantation. The group number, individual number and density-group number of tea plantation decreased due to disastrous frozen snow in 2008 and increased in 2009. However, little influence was observed for the farmland-transformed forestry. [Conclusion] Soil animal community in farmland-transformed tea plantation is interfered by season transition, cold weather's attack, and other disturbances as well. And also, the feedback ability to negative stimulus of ecological environment is relatively poor. In comparison with farmland-transformed forestry, the ecological system of farmland-transformed tea plantation may undergo great potential risk.