While other phone makers are restricting access to their bootloader and making it hard to root your Android phone, the OnePlus 3 has proven to be an island of freedom: with an easily unlockable bootloader and now, an official version of TWRP for the OnePlus 3, rooting your phone is a piece of cake.
Of course, if you have never rooted your phone before, proceed with caution and if you're not sure what you need root for and would rather not deal with terminals, you probably should not root your device.
Let us recap the process of how to root the OnePlus 3. You first start, by unlocking developer options and allowing OEM unlocks and USB debugging. Then, you simply write down the following line "fastboot devices" and then "fastboot oem unlock" in the command line / terminal.
Then, you can proceed with flashing recovery by installing TWRP on your OnePlus 3 and hitting the big install button in the TWRP app. Once you do all this, your phone should be rooted and ready for all your experiments with it. Hit the link right below, to download TWRP for the OnePlus 3. You can also take a look at our in-depth OnePlus 3 review here.
source: TWRP for OnePlus 3