Abstract: Thermal expansion effect of antenna observation pier and bedrock can cause nonlinear change of coordinate time series of global navigation satellite system (GNSS) reference station. In this paper, the effects of thermal expansion on the periodic characteristics of GNSS short baseline time series are evaluated using longterm GNSS observations. The results show that the thermal expansion effect can induce seasonal annual signal of about 1 mm in vertical, and can well explain the periodic signal of GNSS short baseline time series, but has little contribution to the plane direction. However, the effect of thermal bending caused by uneven sunlight irradiation on the plane direction should be considered.