Abstract: Using 5 typical observational curve at sites such as Shihuiyaokou,Hongliuxia,Wozitan,Biandukou and Nanying,in the monitoring area of Gansu Province and its boundaries with Ningxia and Qinghai Provinces,the slow time-varying precursor system is constructed,the abnormity is identified,and the possible relationship between the abnormity and preparation of earthquakes around or over 6.0 magnitude are researched.The results show that at the medium and short-term phase before these earthquakes,the maximum module of latent root exceeded 1.0.This method reduced factitious or experiential identification of abnormity relative to analysis of observational curve,also reflects dynamic variation and adaptive features of precursor system structure for cross-fault deformation.