In this paper, the abnormalities of monthly mean temperature and monthly precipitation in Xi'an for the last 50 years are analyzed by the Morlet wavelet transformation. It shows that the periodic variations are localized in time domain except 1-year natural period and 20~40 years long term variations. Because of the special geographic location, the relationships between the climate variation in Xi'an and ENSO are not strong. The combination of cold or warm and wet or dry climate states are different between long and short time scales. The climate change is regularity on long time scales while the climate variation is random and complicate on short time scales. The temperature variation is mainly random while the precipitation changes with a characteristic scale of 4~5 months.