The invention relates to printing paper transmission equipment used for laser digital developing equipment, in particular to a single-roller bidirectional flat belt tangential exposure paper feeding device. The device comprises a casing body with a paper inlet and a paper outlet, a decelerating motor (7) installed in the casing body and a decelerator (6) matched with the decelerating motor (7). The device is characterized in that an emery roller (1) which is in transmission connection with the decelerator (6) is also installed in the casing body, two sets of matched flat belts are arranged on the two sides of the emery roller (1), and an arc guide plate (4) is arranged between the two sets of flat belts to guide the direction of the printing paper. A lens (5) is installed on the arc guide plate (4), and a through hole is arranged on the casing body corresponding to the position of the lens (5) so as to lead the laser to pass. The device has the advantages of simple structure, easy control and simple maintenance .