Construction method of sliding-descending type rapid pre-supporting system of deep foundation pit

The invention discloses a construction method of a sliding-descending type rapid pre-supporting system of a deep foundation pit. The construction method comprises the following steps of (a) excavating a first layer of foundation pit earthwork, and assembling temporary supporting enclosing purlins with a jacking device; (b) arranging the temporary supporting surrounding purlins in the foundation pit earthwork in a lifting mode through a vertical sliding system, and reserving gaps between the temporary supporting surrounding purlins and the foundation pit earthwork; (c) pushing out the jacking device to the foundation pit earthwork, so that prestress is applied to the foundation pit earthwork for supporting by the temporary supporting surrounding purlins; (d) constructing a reinforced concrete support on the top surfaces of the temporary supporting enclosing purlins, withdrawing the jacking device, and connecting the constructed reinforced concrete support to the interior of the foundation pit earthwork; (e) wh