The 35-year-old actor said he is finding it very difficult to enjoy his life like before, reported Contactmusic.
"He was one of my best friends ever. I find it hard to enjoy life because he's not here... But knowing him, he'd want us to keep smiling and having fun," Gibson said.
Gibson also described his late friend as a joyful person who he never saw "sad" or "crying".
Walker, 40, who was in the passenger, died alongside his friend, Roger Rodas, when their car crashed on November 30, 2013, in Santa Clarita, California.