A detection panel, a manufacturing method thereof and a photo detection device are provided. The detection panel includes a plurality of detection pixel units in an array, the detection pixel unit includes a reflective structure on a base substrate, a detection circuit and a photoelectric conversion structure on the reflective structure; the photoelectric conversion structure includes a first electrode, a photodiode and a second electrode stacked sequentially, and the first electrode is electrically connected with the detection circuit, and the first electrode is an optically transparent electrode, and an orthographic projection of the reflective structure on the base substrate at least covers an orthographic projection of the photodiode on the base substrate.