A direct-lit panel light including a frame, a diffusion plate, a back plate and at least one light bar. The frame comprises a plurality of frame bars that are connected end-to-end, each frame bar having a first mounting surface and a second mounting surface; the diffusion plate is overlapped on the first mounting surface, the back plate is overlapped on the second mounting surface, and the center area of the back plate is fixed with the at least one light bar, and the edge area of the back plate is deformed and forms first convex ribs extending along peripheral sides of the back plate, and the first convex ribs abut against the diffusion plate and press it against the first mounting surface, and the first convex rib on each peripheral side of the back plate has a height gradually increasing from the middle thereof towards two ends thereof, respectively.