Plant told a press conference in London: "I struggle with some of the lyrics from particular periods of time. The musicality and construction of it is peerless.
"Maybe I didn't quite feel the same about the lyrics a little bit later on in life, further on down the road.
"Maybe I'm still trying to work out what I was talking about."
The song begins: "There's a lady who's sure all that glitters is gold/ And she's buying a stairway to heaven."
The three surviving members -- Plant, Jimmy Page and John Paul Jones -- were reunited to promote their new DVD, "Celebration Day". Drummer John Bonham died in 1980.
The DVD is based on their 2007 tribute concert in London to Atlantic Records supremo Ahmet Ertegun.
Led Zeppelin played to packed stadiums and sold millions of albums at the height of their popularity in the 1970s, but they refused to be drawn on their future plans.
When the band were asked whether they might play together again, Page said: "Let me ask you a question. Have you seen the film? Did you enjoy it? Then we've done our job, haven't we?"