The 19-year-old forward joined Arsenal teammate Zac Medley in joining the Gills.
Speaking to the club's website, Evans said: "Trae is a very exciting young talent and he is ready to further his football education.
"He is very highly thought of at Arsenal and his performances have made him a sought after loan player.
"Trae has a lot to learn, his development we are entrusted with but, in reality, his attitude and work rate will determine his success at League 1 level because he is a very very talented boy. He had a vast choice of clubs here in England, Holland and Germany so we are delighted to get the lad here."