how to valid RSS to my site ?

Your RSS should be valid by default.
What did I miss?

https://feedvalidator.org

btw, my feed isnt valid, i think after upgrade to 2.0.1 or 2.0

you can check it here https://feedvalidator.org/check.cgi?url=http%3A%2F%2Fwww.franto.com%2Fblog2%2Fcategory%2Fflash%2Ffeed

there is written i should not use content:encoded inside of feed.

Does anyone knows what is the problem?

After some googling it will seem that Rewlly simple Syndication isn’t Really Simple. There’s some war going on among proponents for different RSS formats.
Regarding the content:encoding some feed readers will not treat it nicely.
More reading nescessary.
The content:encoding encapsulates in your feed a CDATA section, allowing you to have markup like <strong>FlashEarth</strong> in your content, whithout using enities like < and >, and still validate as XML, though I don’t know why you should or should not use content:encoding.

Addendum: RSS History by Dave Winer at Userland.

More on content:encoded.
Here we even have an explanation to the content:encoded markup.