The present invention relates to a device for controlling a hydraulic pump of construction machinery. The device has a first pump supplying working fluid through a swing control valve to a swing motor, and a second pump supplying working fluid through a work tool control valve to a work tool actuator, and includes: a first tilting angle control unit for controlling a discharge flow of the first pump by controlling a tilting angle of the first pump according to an input pump control signal; and a controller deducting a discharge pressure (P2) of the second pump from a discharge pressure (P1) of the first pump to calculate a pump difference pressure-(P1-P2), comparing the calculated pump difference pressure (P1-P2) to a reference difference pressure and, when the calculated pump difference pressure (P1-P2) is greater than the reference difference pressure, outputting the pump control signal to the first tilting angle control unit to make the discharge pressure (P1) of the first pump equal to or less than a first reference pressure that is less than or equal to a swing relief pressure.