Disclosed are a device for fixing acetabular fractures involving the anterior/posterior column and acetabulum quadrilateral plate and a usage method thereof. The device includes an iliopectineal plate and an trapezoidal plate or a pubic plate. The iliopectineal plate and the pubic plate are integrally bent to match with a medial anatomic structure of an iliopectineal line and a superior pubic ramus. The shape of trapezoidal plate matches with the acetabular quadrilateral plate, the anterior column and the posterior column to fix the posterior column, an ischium and the acetabulum quadrilateral plate from inside to outside. The device is at the medial surface of the iliopectineal line, which fixes the fragments of the acetabulum quadrilateral plate in an opposite direction and fixes the acetabular fracture stably for improving the quality of reduction and fixation.