The "Blown away" singer said the couple keeps romance alive by texting constantly, hosting wine and barbecue nights at home and going on dates at Subway.
"We called it 'our place' when we were first dating!" Underwood said.
The six-time Grammy winner is currently in the middle of her eight-month sold-out "Blown Away" tour, but she admits that if her career ever got in the way of her relationship with her husband she would hang up the microphone without hesitation.
"If Mike ever told me he needed me to quit, I'd quit," she says. "When you make that promise to somebody, and you stand before God and your family and friends, you've got to do everything that you possibly can to make that work."
As for how she keep's her slender figure, Underwood revealed Fisher is her biggest motivation.
"Even when he's like, 'I'm so out of shape,' he still has a six-pack," she told People. "Having Mike there – I want to be a hot wife!"