Now, sit back. During the process, the program will unlock your bootloader. You'll see your phone reboot a few times. Keep an eye on it and make sure you don't hit any keys on your phone or computer while the process continues.
After a few reboots, it's time to download and install ClockwordMod Recovery. When it asks if you want to download it, type: Y
After a minute or two, you'll get the following message. It means you've successfully unlocked your phone's bootloader and installing custom recovery.
Next, gain root access to the phone. As your phone boots back up the final time, you'll see it contacting Sprint. This is will re-activate its wireless capability and apply some updates, too.
Be patient. It only takes a couple minutes. Soon, it will display the home screen.
In order to gain root access, use ClockworkMod Recovery to flash the phone's unique root file. Download the file here and copy it to your phone’s SD card.
Now reboot the phone into the bootloader the same way you did before--power down your phone, press, and hold the Volume Down key and tap the power button to turn it back on.
At the top, you’ll see S-OFF on your phone. This confirms you successfully unlocked the bootloader. Use your phone's Volume Up and Down keys to toggle to the Recovery option--select it with the power button.
The ClockworkMod Recovery menu appears. Toggle down to the option: install zip from sdcard. Select it by hitting the power button.
On the next menu, use the power button to select the first option: choose zip from sdcard.
On the next screen, scroll down to the su-184.108.40.206-efgh-signed.zip file. That's the one you downloaded and moved to your SD card earlier.
Press the power button to select it.
Next, install the file. Select Yes. Hit the power button to select it.
After a few seconds, you'll see an Install Complete message.
Now, use the Go Back menu option to get back to the main Recovery menu. Select the option to reboot your phone.
Once your phone boots back up, that's it. You're done. You'll now see the Superuser application in your phone's app drawer. If you like, use an app like Root Checker to confirm you now have root access.
That's all there is to it. Enjoy your newly rooted EVO 3D.