Abstract: In order to study the secondary consolidation deformation and stability of thick soft soil foundation of Zongyang headrace project, this paper selects the undisturbed soft soil samples from Zongyang County to carry out the consolidation test of graded loading and, analyzes the test results, obtains some laws of secondary consolidation deformation of soft soil, and verifies the rationality of the formula by comparing the monitoring data and improving the formula calculation method. The results show that the secondary consolidation coefficient first increases and then decreases with the load, and finally basically stable. It reaches the maximum near the pre consolidation pressure. The secondary consolidation coefficient has a linear relationship with the compression index. The ratio coefficient of the two in the area of water diversion from the Yangtze River to the Huaihe River and Zongyang river is in the range of 0.031 89 ～ 0.041 43, and the secondary consolidation coefficient decays like hyperbola with the logarithm of time;According to the attenuation law of secondary consolidation coefficient with time logarithm, the improved empirical formula of secondary consolidation deformation of soft soil is reasonable.