The Black and Yellow hitmaker, real name Cameron Thomaz, proposed to Rose last year (12), months before announcing they were expecting their first child.
The couple had initially planned to wed in time for Christmas (Dec12), but decided to postpone its plans until after the birth of their baby boy.
Khalifa and Rose welcomed little Sebastian in February (13) and now the stars are preparing to become husband and wife in the coming months, reports Tmz.com.
The licence is valid for 90 days and Khalifa reveals they are aiming for a wedding this autumn (13) - once Rose regains her pre-pregnancy figure.
He tells Sister 2 Sister magazine, "She wants to look perfect in her dress. She doesn't want her dress to fit her 'after baby' body. She wants it to fit her regular body."
The pair began dating in 2010, following Rose's split from fellow new parent, Kanye West.