Elastic-wave velocity estimation in marine sediments with hydrates is an important part of hydrate seismic survey method and engineering. Suspending model and grain contact model are two main hydrate microscopic patterns for the non-cemented sediments with hydrates. Through numerical analysis, we discovered the velocity of compression wave and transverse wave and the Poisson's ratio forecasted by suspending model and grain contact model have bugs in physical understanding. Considering the hydrate microscopic model as the suspending model or grain contact model singly is unreasonable. We point out that the hydrate microscopic model is related with the hydrate saturation and established a modified effective medium modeling of non-cemented sediments with hydrates using the Lagrange interpolation method. This model considers the effect of hydrate saturation on the hydrate microscopic model, and the numerical analysis indicated that the new model is more reasonable. We made numerical simulation of seismic wave field based on the modified effective medium model and studied the characteristics and mechanism of BSR and blanking zone, and then expounded some phenomena observed practically based on the possiblly existing models.