A hydraulic system for wheel type construction machinery, comprising: a hydraulic pump ; a travel motor configured to receive a hydraulic oil discharged from the hydraulic pump to travel the construction machinery; an actuator configured to receive the hydraulic oil from the hydraulic pump to drive a work apparatus of the construction machinery; a travel manipulation portion configured to generate a first pilot pressure for controlling an amount of the hydraulic oil discharged from the hydraulic pump to be supplied to the travel motor , wherein the first pilot pressure generated from the travel manipulation portion is supplied to the hydraulic pump through a pilot line ; a work manipulation portion comprising a joystick and configured to generate a third pilot pressure for controlling an amount of the hydraulic oil to be supplied to the actuator , wherein the third pilot pressure is supplied to the hydraulic pump through a third pilot line ; a sensing portion configured to detect a manipulation change of the travel manipulation portion; a pressure reducing valve installed between the travel manipulation portion and the hydraulic pump to control the first pilot pressure supplied to the hydraulic pump ; a controller receiving information on the manipulation change from the sensing portion, and configured to control an operation of the pressure reducing valve such that the first pilot pressure is gently increased when the manipulation change of the travel manipulation portion is greater than a predetermined value; and a shuttle valve connected to the pilot line and the third pilot line respectively and configured to select and output a higher pressure of the first pilot pressure controlled by the pressure reducing valve and the third pilot pressure, wherein the pressure reducing valve is installed in the pilot line that connects the travel manipulation portion and the shuttle valve . a hydraulic pump ; a travel motor configured to receive a hydraulic oil discharged from the hydraulic pump to travel the construction machinery; an actuator configured to receive the hydraulic oil from the hydraulic pump to drive a work apparatus of the construction machinery; a travel manipulation portion configured to generate a first pilot pressure for controlling an amount of the hydraulic oil discharged from the hydraulic pump to be supplied to the travel motor , wherein the first pilot pressure generated from the travel manipulation portion is supplied to the hydraulic pump through a pilot line ; a work manipulation portion comprising a joystick and configured to generate a third pilot pressure for controlling an amount of the hydraulic oil to be supplied to the actuator , wherein the third pilot pressure is supplied to the hydraulic pump through a third pilot line ; a sensing portion configured to detect a manipulation change of the travel manipulation portion; a pressure reducing valve installed between the travel manipulation portion and the hydraulic pump to control the first pilot pressure supplied to the hydraulic pump ; a controller receiving information on the manipulation change from the sensing portion, and configured to control an operation of the pressure reducing valve such that the first pilot pressure is gently increased when the manipulation change of the travel manipulation portion is greater than a predetermined value; and a shuttle valve connected to the pilot line and the third pilot line respectively and configured to select and output a higher pressure of the first pilot pressure controlled by the pressure reducing valve and the third pilot pressure, wherein the pressure reducing valve is installed in the pilot line that connects the travel manipulation portion and the shuttle valve . <EOS>