Two rock samples with different structures and materials were deformed under a biaxial loading system, and multi-point strain measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using Cv value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of Cv value and to explore its physical meaning experimentally. The result shows that the change of Cv value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. Cv value increases firstly and then decreases before the instability, and the instability occurs when Cv value decreases to the level before increasing. This indicates that Cv value may be a useful parameter for earthquake prediction. Two rock samples with different structures and materials were deformed under a biaxial loading system, and multi-point strain were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using Cv value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of Cv value and to explore its physical meaning experimentally. The result shows that the change of Cv value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. Cv value increases first and then decreases before the instability, and the instability occurs when Cv value decreases to the level before increasing. may be a useful parameter for earthquake prediction.