I'm pregnant at week 37 and my baby weigh 3.4 kg, is that normal or is he huge?

Normal @ 71%tile: We typically consider normal anywhere btwn 10th & 90th percentile, especially when it comes to fetal size, which is always an estimate until delivered & weighed in actuality (ultrasounds are notoriously inaccurate). There are many charts available online. http://www.baby2see.com/medical/charts.html puts your baby @ 71%tile

Likely normal.: If you deliver at 40 weeks, your baby will be "big" but not "huge". While 3-3.6 kg is "average", babies bigger than that are usually perfectly healthy. There is an increased chance of difficulty delivering larger babies, but women do so successfully most of the time. If you're otherwise healthy, specifically if you don't have gestational diabetes, everything should come out fine! Congrats!