The invention discloses a pure light steel joist ceiling, which comprises a terrace base layer, gypsum boards and gypsum lines (4), and a main joist (2). The terrace base layer comprises L-shaped side joists (1) and auxiliary joists (3). The auxiliary joists (3) form skeleton supports of the terrace base layer. The internal corners and/or external corners of the terrace base layer are connected through full-length L-shaped side joists (1). The face layers of the terrace base layer are covered by the gypsum boards and gypsum lines (4) to form an integral ceiling. The auxiliary joists (3) are connected with the main joist (2). The main joist (2) is fixed on the upper interior surface of a room through lead screws (5). The L-shaped side joists (1) and the auxiliary joist (3) are fixedly connected through rivets. The pure light steel joist ceiling has the advantages that the fire protection requirements on the ceiling can be satisfied, the problems of high formaldehyde content and the like caused by using a wood base layer for the ceiling are reduced, and a series of common quality problems such as cracking, deformation, corrosion and damages by worms caused by using the wood base layer can be solved.