A dual roll blind system is able to adjust a light shading rate or extent and comprises a winding roll which includes a roll casing rotatably supported between both side plates of a ceiling bracket; a driving winding roll which includes a moving member disposed between both side plates in parallel with the winding roll and is thread-engaged with a screw shaft rotating by means of a blind winding device of one side, a straight moving member which is provided for left and right straight movements by restricting the rotation of the moving member, and a roll casing engaged with the moving member and the straight moving member; a first blind material of which upper end is fixed at the winding roll and in which a light transmission part and a light non-transmission part having constant widths are alternately formed in a width wise direction; a second blind material of which upper end is fixed at the driving winding roll and which has a light transmission part and a light non-transmission part corresponding to the first blind material and is movable left and right; and a counterweight bar which fixes a lower end of the first blind material with a lower end of the second blind material being slidably inserted into the counterweight bar in a parallel direction.