Abstract: The in-situ tests on extra long cast-in-place pile were conductyed by self-balanced loading tests in the area of contiguity to the sea in Tianjin.The length of the piles was above 90 m.The distribution of axial force of piles was related to the position of loading boxes in the tests.The bearing capacity of piles was lost under the condition of small total displacement.The lateral friction of piles developed with small displacement mutably.At the same time,the tip resistance could not develop.So the tip resistance should be cautiously considered when the bearing capacity of extra long piles was designed.