The time series data with multiple frequencies which are collected by using audio frequency magnetotelluric method (AMT) often contain interference signals. After a lot of measured time series data viewed, we have found that the data are seriously interfered by adjacent source, but the interference signal appearance is not continuous. According to the features of the interference signal and the analysis result of original data format of V5-2000 magnetotelluric instrument, the author proposed a method for automatic selection of time series data. Real data processing results in Ningwu area show that this method can partly suppress the adjacent source interference.