The invention discloses a device for cleaning soil between the piles of a long screw pile-reinforced soft soil layer roadbed and a cleaning method, and solves the problems that the cleaning workload of the soil between the piles is high and the shape and size of a cast-in-place pile cap are difficult to control. The device for cleaning the soil between the piles is assembled firstly, and then thedevice is used for carrying out mechanized cleaning work on the soil between the piles; a drive motor (3) is started to cause the output shaft of the drive motor to drive a lead screw (8) to rotate clockwise, a lead screw nut (9) rotates downwards to move, a sleeve (13) rotates to be sleeved on a pile head (12), five pieces of spiral cutting blades, which are in an equal interval radian, are welded on an outer side wall of the sleeve, and a soil body around the pile head is dug out to form an outer ring direction operation space of the pile head; the control power source of the drive motor isswitched on in a reverse direction so as to cause the output shaft of the drive motor to drive the lead screw to rotate anticlockwise, the lead screw nut rotates upwards to move along the lead screw,and the sleeve is driven by the lead screw nut to move upwards while rotating so as to switch off the power source of the drive motor. The method has the characteristics of high construction efficiency and low cost.