Method for reducing trapped pressure of ultrahigh density narrow window saline layer

The invention discloses a method for reducing the trapped pressure of an ultrahigh density narrow window saline layer. The method comprises the following steps that (a) well overflowing occurs, a pump is shut down, a well is closed, whether the saline layer is entered or not is judged according to logging data and an on guard record, and the pressure of a sleeve is recorded; (b) when the saline layer is confirmed to be entered, contaminated drilling liquid is discharged; (c) drilling liquid performance is circularly adjusted to meet the downhole requirements, then the well is closed, and the pressure is calculated; (d) when the sleeve pressure is larger than or equal to 5 MPa at this time, pressure controlling and water discharging are conducted, and if the sleeve pressure is smaller than 5 MPa, natural water discharging is conducted; (e) after water discharging, drilling liquid contaminated because of water discharging is circularly discharged, the well is closed, the pressure is calculated, and the well is