The invention discloses a small radius spiral stair glass railing installing structure. The installing structure comprises a railing part, first fixing parts and glass plates; the railing part is fixedly installed on a stair platform; each first fixing part comprises a body part and an extending part, wherein the extending part is arranged perpendicular to the body part and provided with a thread section, the thread section is in threaded connection with the stair platform, and at least one groove perpendicular to the extending part is formed in the body part; the glass plates are clamped into the grooves and fixedly connected with the railing part through second fixing parts. Compared with the prior art, a small radius spiral stair glass railing can be installed more easily, efficiently, accurately and safely.