Deep foundation pit earthwork digging method

The invention relates to a deep foundation pit earthwork digging method. The method comprises the following steps of: (1) after paying-off measurement of a deep foundation pit is finished, designing N layers of horizontal supporting steel plates according to the deep foundation pit engineering conditions in the deep foundation pit from top to bottom, and digging the foundation pit earthwork layerby layer by adopting an island type digging method, wherein N is more than or equal to 1 and less than or equal to 20; (2) downwards driving an outside steel plate pile along the wall of the deep foundation pit; and (3) digging the earthwork above the first layer of horizontal supporting steel plate, welding one end of the first layer of horizontal supporting steel plate to the outside steel plate pile, downwards driving an inside steel plate pile at the other end of first layer of the horizontal supporting steel plate and the like, constructing the Nth layer of horizontal supporting steel plate, building a ramp, digging the earthwork below the Nth layer of horizontal supporting steel plate, regressing, digging the ramp, removing the inside steel plate pile, digging the rest earthwork, and thus finishing digging the earthwork of the deep foundation pit. The construction method is simple and feasible; a trestle is not required, the construction period is effectively quickened, and the digging cost of the earthwork of the deep foundation pit is reduced; and the deep foundation pit earthwork digging method is safe and reliable.