Based on the Mindlin elastic displacement solution and combined with finite element numerical example, the analysis is made on the vertical deformation difference of deep plate test and single pile vertical compressive static load test under the same load condition. The ratio of vertical displacement resulted from these 2 tests decreases with the increase of pile diameter, and the ratio is 3.2～4.6 while the conventional pile diameters are within the range of 0.8～2.0m. The engineering example shows that the ratio of the both can be 4.5～7.2 times. Therefore, single pile vertical load-bearing potential can not be fully exploited in the deep plate loading test and the test results can not truly reflect the single pile vertical load-bearing performance. The bearing capacity of pile tip should be determined by single pile vertical compressive static load test rather than deep plate loading test.