The invention discloses an OLED display panel and a preparation method. The OLED display panel comprises a glass substrate, a first bottom gate, a light shielding layer, a buffer layer, a first polycrystalline silicon layer, a second polycrystalline silicon layer, a gate insulating layer, a first top gate, a second top gate, an interlayer insulating layer, a first source electrode, a first drain electrode, a second source electrode, a second drain electrode, a passivation layer, a planarization layer, a pixel electrode, a pixel definition layer, an OLED light-emitting device and a cathode metal layer. The first source electrode is in contact with the first bottom grid electrode through a via hole, and the second source electrode is in contact with the light shielding layer through anothervia hole.