The invention discloses a high-efficiency high/medium pressure gland casing structure for a steam turbine. The high/medium pressure gland casing comprises a gland casing high-pressure steam inlet end molded line and a gland casing high-pressure steam outlet end molded line on a high-pressure side, a gland casing medium-pressure steam inlet end molded line and a gland casing medium-pressure steam outlet end molded line on a medium-pressure side, and is characterized in that the gland casing high-pressure steam inlet end molded line is matched with a high-pressure side cylinder molded line; the gland casing high-pressure steam outlet end molded line is matched with a high-pressure primary separator inlet; the gland casing medium-pressure steam inlet end molded line is connected with a medium-pressure side cylinder molded line; the gland casing medium-pressure steam outlet end molded line is connected with a medium-pressure primary separator inlet, so that the cylinder respectively forms a smooth steam inlet runner from the high/medium-pressure steam inlets to the high/medium-pressure primary separator inlets. The gland casing structure disclosed by the invention can form a complete and smooth steam runner capable of rotating by 360 degrees and has extremely high steam inlet frequency.