Speaking to TV Choice Magazine, Miller suggested that the pair have a good chemistry because they know each other well.
"I think it's our long-running friendship," he said. "The friendship is more important than comedy. Most of what Xander and I talk about is not comedy, it's just normal everyday stuff, friends we've got in common, things like that.
"Our experiences are quite common because we have both got young families. There is lots of shared history, so I think it's that."
Miller also revealed that he expects to work with Armstrong for some time.
"It's very hard to think beyond where you are at this moment," he said. "I think we certainly feel like there is plenty of lead in our pencils. We certainly feel there is a lot of stuff we want to do."
The new series of The Armstrong and Miller Show begins on Saturday at 9.45pm on BBC One.