Accurate assessment of local myocardial contraction is important for diagnosis of ischemic heart disease, because decreases of myocardial motion often appear in the early stages of the disease. Three-dimensional (3-D) assessment of the stiffness distribution is required for accurate diagnosis of ischemic heart disease. Calculation of displacement's spatial derivation is a necessary step in myocardial strain imaging system, but it is very sensitive to noise. In order to improve the accuracy and contrast of strain image, we propose a novel displacement smoothing method: dynamic grid interpolation method. From the simulation results, we can see that the strain images' accuracy have been improved 7.01%, and the contrast have been improved 20.80%.