The fine soil filler contained in the subgrade of heavy haul railway will produce large deformation under the repeated action of train load, which will affect the safety of train operation. The train load is regarded as a continuous dynamic load in previous triaxial tests without considering the time intermittent effect. In order to investigate the accumulative plastic deformation and its dynamic and hydraulic characteristics of silty subgrade soil with different dynamic stress amplitude, water content, loading vibration times, intermittent time and relative coefficient (the ratio of intermittent time to loading time), drainage conditions, an intermittent cyclic loading dynamic triaxial test is carried out. Through the analysis of the test results, a method for determining the critical dynamic stress and critical moisture content of the soil by bilinear method is proposed, the critical dynamic stress ratio (the ratio of critical dynamic stress to confining pressure) changes linearly with the moisture content is found. It is found that the longer the loading interval time and the less the loading vibration times and the larger the relative coefficient, the smaller the accumulative deformation of the soil. And with the optimization of drainage conditions, the accumulative plastic deformation of the soil decreases in turn, the strength increases sequentially. The above research provides a theoretical reference for evaluation of hydrodynamic stability of heavy haul railway subgrade and rational selection of train interval time.