We have already proposed the real-time strain imaging techniques (ca. 12 fps) for stable diagnosis in freehand and image classification method for the breast tissue diagnosis. For the objective diagnosis, most important problem is come from the fact that the strain image patterns were strongly depending on the magnitude and uniformity of the compression. In this paper, we investigate the pressure-distribution effects on the elasticity imaging using the tissue-mimicking elastography phantoms. We prepared 5 types of elastography phantoms with different stiffness. Phantoms #1-#3 have uniform stiffness overall in the rectangular solids and #4-#5 include small rectangular solids with different stiffness from surroundings. The phantom stiffness was estimated from the distribution of pressure and induced strain using our elasticity imaging system as follows. (1) The Young's moduli of first three phantoms were estimated as 6±1 kPa, 27±4 kPa, and 108±23 kPa, respectively. (2) In the case of phantoms #4 and #5, outer parts were estimated as 6±1 kPa and 8±2 kPa, and inclusion parts were measured as 12±1 kPa and 58±14 kPa, respectively. (3) For the special case of above phantom #1, we applied non-uniform pressure (3 times difference between each lateral limits). Even in that case, we successfully reduced the effect of non-uniformity from 235 % to 5 % in elasticity imaging.