The invention provides a pile prepressing method of a four-pile-leg self-elevating platform. The pile prepressing method comprises the steps that S10, platform pile inserting locating is carried out; S20, a platform main ship body is kept in a state of floating in seawater, two pile legs on one diagonal line of the platform are in a supporting state so as to keep relatively fixed with the main ship body, and meanwhile two pile legs on the other diagonal line are in a lifting state so as to descend relative to the main ship body so that the two pile legs can be pressed down towards the seabed; and S30, the ascending and descending state of the main ship body is monitored, when the main ship body slightly ascends, the two pile legs originally in the lifting state are converted to the supporting state, the two pile legs originally in the supporting state are converted to the lifting state, and the step is repeated till the load of each pile leg is not smaller than a load set value. According to the method, the work time of pile prepressing can be shortened, and the work safety of pile prepressing can be improved.