The station is served by the Hanwa Line of West Japan Railway Company (JR West) and the Midōsuji Line of Osaka Metro; the former uses elevated tracks and the latter uses underground tracks.

When it was located on the ground level, Nagai Station had two island platforms serving 2 tracks each.

The station is currently elevated (northbound in 2004, southbound in 2006) and has two side platforms serving a track each.

The station has two side platforms serving two tracks on the second basement.

Ticket gates are located in the north and the south on the first basement.