Abstract: Before an earthquake,the velocities of elastic waves observed at different stations usually have different values. This phenomenon suggests that the spatial distribution of the variations of rock properties is inhomogeneous before the failure of rocks. The precursors to failure in rocks should come from the changes of the spatial distributions (physical fields) of the rocks.The process of spatial variations in the travel times of P-wave in the rock under uniaxial stress is studied. The experimental results show that the long-term precursor of failure of rocks is characterized by synchronism in variations of the P-wave velocities,and the short-term precursor by nonuniformity. The process of the rupture in rocks is the evolution process from disorder to order in the spatial distributions of the vairations of physical properties of rocks,or the process of the decrease in entropy.