Abstract: The advantage and feature of digital observation is the increasing in sampling rate.Based on the feature that digital data has high frequency information,the variations of digital subsurface fluid data before and after Longyao M_L5.4 earthquake(Apr.22,2002),Huailai M_L4.4 earthquake(Aug.3,2002),Luanxian M_L5.0(Jan.20,2004) are analyzed with primitive curve method and anomaly frequency method.The results show that anomaly frequency method is effective for the analysis of high frequency information characteristics in digital subsurface fluid data.