Abstract: To study the influence of column height ratio (namely the ratio of column heights of two columns with different heights) on flexural and torsional performance of Unequal-Height RC Double-column pier along bridge direction, quasi-static loading tests were carried out on two Unequal-Height RC Double-column piers with different column height ratio under the combined action of compression, bending and torsion. The shear-displacement hysteresis curves, torque-torsion hysteresis curves and corresponding skeleton curves of the double-column pier were obtained. Based on Abaqus, the finite element model of Unequal-Height RC Double-column pier was established, and its accuracy was verified by experimental results. Then parametric analysis was carried out to study the effects of column height ratio, axial compression ratio and stirrup ratio on the seismic performance of unequal-height double-column pier under the combined action of bending and torsion. The results show that the reduction of column height ratio increases the flexural bearing capacity along bridge direction, and reduces the torsional energy dissipation and torsional bearing capacity of the specimens. With the decrease of the column height ratio, the torsional effect is enhanced, which reduces the ductile deformation capacity of the double-column pier and enlarges the damage area of the unequal-height double-column pier. In order to avoid the bending shear failure of the short column of the unequal-height double-column pier, the column height ratio is recommended to be no less than 0.67. With the increase of axial compression ratio, the flexural capacity of unequal-height double-column pier under the combined action of bending and torsion is decreased. The torsional bearing capacity of specimens can be significantly improved by increasing the hoop ratio; therefore the hoop ratio can be appropriately increased for the unequal-height double-column pier that may be subjected to torsion.