There are many that have still not rooted their Sony Ericsson Xperia X10 handsets mainly due to the perceived complexity involved. Ever since the root for the Xperia X10 was first announced the process has got easier and easier. The recently announced Exploid root method for the X10 mini and X10 mini pro handsets already works perfectly for the Xperia X10, but now an even simpler method has emerged.
All you have to do is download and install the UniversalAndroot apk. Once installed, all you then do is click the root button and you should have a rooted handset. The apk also has an unroot button, so if you don’t want it for whatever reason you can always revert back. The benefits of rooting are numerous and include being able to run root-only apps such as Titanium Backup and Barnacle Wifi Tether that turns your X10 into a wireless hotspot.
Visit here to download universal androot.apk> http://forum.xda-developers.com/showthread.php?t=747598
Alternate: x10root > http://forum.xda-developers.com/showpost.php?p=7552418&postcount=133