Based on NCEP reanalysis data and OLR data from NOAA, the characteristics and the causes for the rainband anomaly over the southern China in June 2003 are studied. The results show that exceptional weak ITCZ over the West Pacific Ocean and the fewer tropical cyclones make subtropical high continually stay in the south area; the monsoon circulation is influenced by the convective anomaly over the southern Tibetan Plateau and the low-latitude ocean, thus the moisture is concentrated to the low-latitude area and the southwest monsoon moisture transfer passage is to the south of its normal location; the ridge line of the south Asian high is prevented by the middle and high latitude circulation anomalies at high levels from moving northward, moreover, the west wind front at lower levels is intensified by west wind anomalies at high level through momentum downward transfer. All the facts mentioned above give the reasons for the rainband anomaly.