The House That Built Me singer wed Shelton in May, 2011, but distance almost drove them apart as Lambert was away on tour while her husband was in Los Angeles filming reality Tv show The Voice.
Their busy schedules meant they spent little time at home in Tishomingo, Oklahoma together, and Lambert admits there were "a million" moments when she questioned whether their marriage would last a year.
She tells Redbook magazine, "The first year was really hard."
She claims the country couple made it by setting down some rules to keep the romance alive.
And when it came to celebrating her first anniversary as Mrs. Shelton, Lambert says, "It was like, 'Ah, we made it'. It's been great since."
The couple now never spends more than two weeks apart and Shelton and Lambert allow one another to snoop through their cell phones.
She adds, "It just takes the question out of the marriage."
And Lambert, who has previously declared "divorce is not an option", loves to bond with her husband at home over their shared love of food and drink.
She adds, "We hang out on the porch, drink beer and cook burgers. I think it's important as a married couple to be friends."