The girl group were signed to the X Factor judge's record label Syco upon winning the competition in December and have since been working on their debut album.
However, the four-piece - consisting of Perrie Edwards, Jesy Nelson, Leigh-Anne Pinnock and Jade Thirlwall - admitted they were nervous when they had to play their new single to Cowell for the first time.
"We had a meeting with Simon three weeks ago so he could listen to the track, and it was like sitting in the headmaster's office," Nelson told the Daily Star.
"We were so nervous before going in, it was surreal."
Thirlwall added: "He really liked it. He's happy with the progress we've made in such a short time and just wants us to be as successful as One Direction.
"The album's going to be so different. No-one's expecting what it sounds like."
Little Mix recently told Digital Spy that their new single is "quite old-school" and that they will be "bringing back the old harmonies".
> Little Mix to release autobiography
Watch Digital Spy's recent interview with Little Mix below: