An X-ray flat panel detector, a method for manufacturing the X-ray flat panel detector, a detection device and an imaging system are provided. The X-ray flat panel detector includes: a substrate; a back plate layer arranged on the substrate and including a plurality of thin film transistors, each thin film transistor including a source/drain electrode layer; a wiring layer arranged at a side of the back plate layer distal to the substrate and including a plurality of connection lines; and a photosensitive element layer arranged at a side of the wiring layer distal to the substrate and including first electrodes. Each first electrode is electrically connected to the source/drain electrode layer of a corresponding thin film transistor through a corresponding connection line, and an orthogonal projection of the first electrode onto the substrate does not overlap an orthogonal projection of the corresponding thin film transistor onto the substrate.