The invention provides a flat-plate solar air collector, which comprises a cover plate (2), a bottom plate (6), an absorber plate (4) arranged between the cover plate (2) and the bottom plate (6) and a transparent partition plate (3) arranged between the cover plate (2) and the absorber plate (4), wherein air flows in from a first preheating layer which is formed by the cover plate (2) and the transparent partition plate (3). By the flat-plate solar air collector, heat loss can be decreased, and collecting efficiency can be effectively improved.