The invention discloses a dismantling construction process for foundation pits in water area, which is mainly to dismantle supports at four supporting docking blocks at first during the construction of a dock entrance bed-plate and docking blocks. After the construction of a dock entrance structure is finished, the first stage dismantling task is performed, steps of the first stage are as follows: the dismantling period begins after the construction of a dock entrance threshold, docking blocks and granite is finished, the dismantling sequence is from the bottom up, a third support and a second support are orderly dismantled, front-edge slope protection is cleared up, a first concrete support and a river-side breast wall are dismantled, vertical columns are hoisted, steel sheet piles is pulled out, underwater dredge is carried out, front-edge steel sheet piles are cut off, and a dock entrance bed-plate is cleared up. The second stage dismantling task is carried out, the dismantling period begins after a dock gate is closed, the dismantling sequence is from the bottom up, a bank-side breast wall, a first concrete support, a second concrete support and a third concrete support are orderly dismantled, bank-side steel sheet piles are cut off and the dock entrance bed-plate is cleared up. The construction process is scientific and reasonable, steps are simple and easy to realize; moreover, the construction process can avoid the dock entrance structure from being damaged during the whole construction process, save the energy consumption, and protect the environment.